Inferno (TV story)

Inferno was the fourth and final serial of season 7 of Doctor Who. It was the final regular appearance of Caroline John as Liz Shaw, although her departure is not depicted. It was also the first Doctor Who story to explore the concept of parallel universes.

Inferno was the first story in which producer Barry Letts had any say on development and commissioning. Director Douglas Camfield suffered a minor heart attack after completing the location filming and the studio scenes for episodes one and two. This left Letts to direct the studio scenes for the remaining five episodes.

Several possible stories were considered for the season finale. The Mists of Madness by Brian Wright and The Shadow People by Charlotte and Dennis Plimmer were two. However, Wright was unavailable, and the Plimmers abandoned the project after a pay dispute. This left the way open for The Mo-Hole Project, as it was then titled, by Don Houghton. The serial went through several name changes before becoming Inferno.

Houghton had based the drilling part of the story on real events. He had contacted the American Embassy to enquire about, a real world attempt to drill through the Earth's crust. Information on the project and why it was abandoned were not disclosed as such information was top secret. It was this secrecy that Houghton developed for his story.

Letts was worried when the first script draft arrived as he did not think there was enough in it to fill a seven-parter. Additions such as the Primords and scenes featuring Venusian aikido were made to suitably lengthen the script.

Synopsis
UNIT is providing security cover at an experimental drilling project designed to penetrate the Earth's crust and release a previously untapped source of energy. Soon, however, the drill head starts to leak an oily green liquid that transforms those who touch it into vicious primeval creatures with a craving for heat.

The Doctor is accidentally transported by the partially repaired TARDIS control console into a parallel universe where the drilling project is at a more advanced stage. Thwarted by his friends' ruthless alter egos, he works to save both universes.

Episode 1
The Doctor drives Bessie into an area marked restricted.

A maintenance worker by the name of Harry Slocum enters a drilling unit nicknamed Inferno. He introduces himself to Sir Keith and is told there is an issue with pipe number two. He is urged to fix it quickly, as Professor Stahlman does not want any delays. The Professor is at loggerheads with Sir Keith and tells him he should never have stopped the pipe for maintenance. He tells Sir Keith never to make a decision with regards to the drilling again.

As Slocum is fixing the pipe, he sees a green goo emanating from the base. He touches it, and it burns. He is horrified to see his hand turn green.

Sir Keith discusses the Professor with his personal assistant Petra. He confides that he has sent for an expert in oil rig mining, Greg Sutton, as he is nervous that there is no one with real drilling expertise on the mission.

As Slocum leaves, he seems entranced. He heads outside the complex and stumbles against a piece of scaffolding. A man rushes out to help him. With a growl Slocum turns on him and kills him with his wrench.

In a room inside the complex, Benton is hanging a picture in what is to be the UNIT HQ. The Brigadier enters and asks if there has been any sightings of Slocum. Benton says there hasn't been. The Doctor enters, and the Brigadier tells him of the murder. He shows him the wrench. It is still warm and, when it was found, it was red hot. The Brigadier comments that trouble seems to follow the Doctor around, and he questions why he asked to be on this mission. The Doctor says that an opportunity to be at the first penetration of the Earth's crust was not to be turned down. He heads off to do some experiments of his own.

Sutton has arrived and is bewildered at having been pulled over with such urgency. Sir Keith shows him around the complex. He says that the drill head is twenty miles deep. This has been achieved by having no pipes, the pipes visible containing coolant delivered to the drill bit. Instead, there is a robot drill that is fed by a cable from a nuclear reactor. Sutton asks what this is hoping to achieve. The project is aiming to pipe Stahlman's gas (named after the Professor), a powerful energy source trapped inside the Earth's crust since the dawn of time. Sir Keith begins to introduce Sutton to the staff. He tries to flirt with Petra and is snubbed. On introduction to the Professor, he is cold. The Professor thinks that Sir Keith is trying to introduce as many experts into the project as he can to try to close it down. He counts the Doctor as one of these. Sir Keith introduces Sutton to the Doctor and asks his opinion on the project. He says that they should be heeding the warnings of the computers. As he leaves, he overhears the Professor complaining about the experts to Petra. He causally, but loudly, points out a flaw in the mechanics to a near by scientist, causing the Professor's blood to boil.

The Doctor pulls up to a small building being guarded by a UNIT soldier. He asks if there is any news about Slocum; he is told that there isn't. The Doctor uses a device to open the door to the building remotely and drives Bessie in. Liz is inside working on the TARDIS console. The Doctor hands over the figures from the computer and tells her of the murder. She already knows as the sentry told her. They discuss the real reason they are here. The Doctor wants to use the nuclear power to try to jump start his TARDIS console. He wants a test run straight away. Liz starts flicking switches and positions herself by the main switch.

Slocum is skulking around the complex. He is now covered in hair and has claws. He enters a building. A member of UNIT is on the phone. Slocum approaches him from behind.

The Doctor says he is ready. Liz pulls the lever down. The machine registers 7 mega volts.

Slocum has killed the UNIT soldier. He pulls a switch down to maximum.

The console begins to shake. The Doctor says that there is too much power. Liz cannot do anything as the circuits are locked. The console and the Doctor dematerialise.

The Doctor is in some kind of limbo and is in some pain as he and the console fly through the darkness. He flies off into the black.

Liz uses a plank of wood to force the levers down.

The Doctor and the console reappear. The Doctor is groggy but fine. He is keen for another trial run. Liz tries to dissuade him, but he says he needs to know where he was. An alarm goes off. It is the drill head. The Doctor and Liz hurry off to Bessie.

The complex is in lock down as the drilling room fills with smoke. The Professor argues with Sir Keith as to why he ordered the lockdown. Sir Keith implores him to shut off the power, but he refuses. Sutton says that if the power is stopped now, it will never be able to be restarted again. Petra is ordered to check the coolant. Sutton tries to stop her, saying that the pressure is too dangerous, but she doesn't care. The Doctor and Liz enter. The Doctor says that there has been a nuclear power surge. The Brigadier enters and says that there has been another murder. The Doctor goes to the Professor to give him his advice, but he tells him to stop wasting his time. The Doctor heads off with the Brigadier. Petra returns, saying that the controls are jammed with the heat. Suffolk tries to stop her from heading off but instead goes with her to help. They find the Professor trying to stop it manually. Sutton helps.

The Doctor and the Brigadier go to examine the body. As they do, Slocum jumps up, growling.

Episode 2
The Doctor stops any UNIT forces from attacking.

Sutton has sorted the issue with the coolant. The Professor says the readings are too high. He gets offended when Petra suggests they need the Doctor.

The Doctor tries to calm Slocum. A UNIT soldier, Private Wyatt, sneaks up on Slocum and prepares to attack.

The Professor is trying to contact the Doctor.

The phone is ringing but all ignore it. Slocum attacks Wyatt. Wyatt manages to shoot him twice. They wrestle, and then Slocum slumps to the ground.

Sir Keith wants to stop the drilling, but the Professor blocks it.

Slocum is wounded but alive. The Doctor wants to turn off the switch but can't as it is too hot. He borrows the Brigadier's gun and uses that. Slocum dies. As he slumps down, the wall he was leaning on is blackened and scorched. The Doctor answers the phone and tells the Professor he has sorted everything.

The Professor tells his workers to return to their duties. Sutton is cross at him and says he is just asking for trouble. He tries to confide with Petra and implores her to try to persuade the Professor.

The Doctor and the Brigadier examine the body. He was shot twice through the heart but remained alive for several minutes. The Doctor marvels at his abnormal resistance and strength. The body is still hot. The attacked UNIT scientist and Private Wyatt are seemingly fine.

The Doctor and the Brigadier climb to the roof to discuss what is going on. The Doctor suggests that there is some kind of retrogression of body cells that causes the victim to turn into animals. The Doctor says that it is a very slow process and wasn't complete with Slocum. The Brigadier asks if he has ever heard a noise like the one Slocum made. The Doctor says he has, at Krakatoa in 1883. The Brigadier asks if there is a link. They are interrupted by a UNIT soldier, who reports that Wyatt has disappeared. The Brigadier and the soldier rush off to find him. The Doctor sees him high above on a walkway and pursues him. When he catches up, Wyatt is animalistic. He approaches the Doctor, wielding his gun like a club. He swings too hard and throws himself off the edge of the walkway. The Doctor shouts for no one to touch him.

The UNIT scientist emerges from the building in a trance.

The Professor wants to increase the drilling speed. Petra calls him into a room where Sir Keith and Sutton are examining something. They open a box and show the Professor a vial of the green goo. Sir Keith says that it has defied analysis and that it is very tricky to analyse as it is too hot and does not cool down. The Doctor tries to suggest what it is, again mentioning Krakatoa. The Brigadier wants to talk to the Professor and Sir Keith. The Professor is reluctant to comply. The Brigadier insists. Left alone, Liz and the Doctor discuss the substance. The Doctor says he wants to hear it as he thinks it will let off a scream. Liz asks him to come and look at one of the computers.

The Professor is callous and is not bothered about the deaths on his site. The Brigadier and Sir Keith plead with him to show more mercy. He says he has no time for these deaths nor any crazy theories of the Doctor's. The Doctor enters and asks if the Professor ever intends on paying heed to his computers. The Professor insists that the computers are over sensitive. The Doctor reacts angrily. Petra rushes in and says that the vial holding the green goo is about to break. The Professor strides out and, against the Doctor's suggestions, takes the vial in his hands and puts it back into the box. He orders it to be deep frozen. The Professor makes it clear that his discussion with the Brigadier is over and that the computer is faulty. The Doctor shows the Professor the computer and warns him that he should stop the drilling. Again, the Professor says that the readings are inaccurate. The Doctor goes to leave. The Professor tells him that he is taking away the nuclear power that he has been using to experiment with the TARDIS. The Doctor tells him that he is being childish. The Professor tells Petra that they can up the work rate of the drill in 25 minutes. Petra asks if it is safe, but the Professor disregards her. As he is left alone, he discovers that his hand is green.

The Doctor asks Liz to go back to their hut and test the tri-gamma circuits on the console. Subtly he flicks a switch on one of the computers and closes his hut back up.

The Professor enters and opens the computer and removes a microcircuit. He finds a truncheon in the Brigadier's desk and goes to smash it. The Doctor stops him. He goes to do it again, and the Doctor uses Venusian aikido to paralyse him. The Brigadier breaks it up. The Professor leaves, saying that the Doctor is a mad man. The Doctor tells the Brigadier what he saw. When they challenge him, the Professor accuses the Doctor of trying to sabotage the drilling. They check his pockets, and he no longer has the microcircuit. As the Doctor leaves, he points out that the computer has already stopped working. Unseen, the Professor stamps on the microcircuit which he had dropped on the floor.

The Doctor returns to his hut. Liz has fixed the tri-gamma circuits. She asks why he asked her to do it, and he says he strongly believes that the console is fine; it is just the nuclear surge that ruined his test. Liz says she is relieved they can't test again. The Doctor sends Liz off to run some tests through the computer. As soon as he is alone, he busies himself with the console.

As Liz leaves, she is pursued by the animalistic form of the UNIT scientist.

Liz returns to find the computer broken. When she explains to the Brigadier why she is there, he says that the Doctor knew the computer wasn't functioning. Liz rushes over and sees that the switch to provide power to the Doctor's hut is on. She and the Brigadier run off.

The Doctor hangs onto his console as it begins to shake.

The Professor notices that the power is down. He runs over to the switch and switches the Doctor's power off.

Liz and the Brigadier return to see the Doctor and his console dematerialise.

Episode 3
Liz tries to bring back the now disappeared Doctor, but there is no power. He is trapped.

Liz and the Brigadier return to the base. The Brigadier orders the Professor to reconnect the power and explains why. He refuses. Sir Keith threatens to tell the Ministry about this and the new mining speeds. The Professor tells him to do so. When the Professor leaves, Sir Keith says he will go to London as soon as possible but can't leave the Professor to do as he pleases at this critical point of the drilling.

The Professor's hand is now bright green. As he puts some gloves on, he is seen by Petra, who tells him to get it checked. He tells her not to worry.

Liz berates the Brigadier for not showing concern over the Doctor. The Brigadier says he has many concerns of which the Doctor is one.

The Doctor awakes. His surroundings are somewhat altered. On the wall is a poster that reads "Unity is Strength". His device does not open the door, so he forces it open. The shed door has a sign reading "Technical Store" with an unfamiliar logo on it. He drives Bessie out of the garage and pauses to close the door when he is shot at by soldiers. After protesting, he jumps aboard Bessie and drives off, pursued by the soldiers, who consider him a saboteur. He soon finds himself in a dead end where a soldier jumps aboard Bessie. The Doctor and the soldier fight as the Doctor drives. He manages to throw the soldier out of the car. He parks Bessie between some houses and hides in a bin. The pursuing soldiers run into the house, allowing the Doctor to escape. The Doctor sneaks onto a walkway above the compound and watches the soldiers look for him. He hears a snarl behind him, and one of the animalised humans approaches him. As he attacks, the Doctor uses a fire extinguisher to subdue him. This draws the attention of the soldiers, who continue to pursue him. Another animalised human approaches him. The Doctor counters his attack with a wooden pole.

Below, the soldiers are ordered to shoot on sight. They see a figure above them and shoot. The animalised human falls to the ground.

A female figure marches though the compound. The Doctor sees that it is Liz, only with a different haircut. The Doctor draws attention to himself and asks why she is wearing those clothes. The woman looks confused, draws a gun and blows her whistle for backup. She orders they take him away.

The Doctor is brought into the Brigadier's office, where he is met with a figure similar to the Brigadier but with an eyepatch and a large scar by his eye. He asks how the Doctor got in. The Doctor responds quizzically and asks who he is. The man reveals himself to be Brigade Leader Lethbridge-Stewart, while the woman is Section Leader Elizabeth Shaw. When he asks who the Doctor is, the Doctor realises what has happened. He introduces himself as Doctor John Smith and says he is from a parallel space time continuum. The Brigade Leader is unsure if he is mad or bluffing. The Doctor shows he has knowledge of the drill and the people running it. He wants to see Professor Stahlman or Sir Keith. The Brigade Leader takes him to Director Stahlman.

On the way, the Doctor notices that the drilling is three hours and twenty minutes away from the core, much in advance of where the Doctor has come from. When the Doctor is brought to the Director, he asks to see Sir Keith. The Director tells him that Sir Keith was killed in a car accident on the way to the ministry in London. The Doctor draws attention to the broken computer that was giving out warning signs before it broke down. The Director accuses the Doctor of having broken it and calls him away. He turns to Doctor Petra Williams, the Assistant Director of the project, and asks her to continue the drilling. Sutton tells her that there is no pressure getting to the drill head. Doctor Williams tells him that she is aware of this. Doctor Williams tells the Director what Sutton told her. He refuses to decelerate. Once he is left alone, he feels a pain in his hand. He takes off the glove, and it is bright green all over and hairy.

The Doctor is being made to wait by the Brigade Leader. He asks what is going to happen to him and is told that he will be executed without trial under the Defence of the Republic Act 1943. When the Doctor asks about the royal family, he is told that they were executed. When the Doctor tries to sit down, he is forced to his feet by the soldiers. When he badmouths them, the Brigade Leader tells him he cannot insult the Republican Security Forces who have been brought here to protect the drilling. The Doctor says they will need protecting if the computer that was giving out danger signals or the death of Harry Slocum is anything to go by. The Brigade Leader says he is showing the amount of knowledge that only a spy could possess. The Doctor insists that he has seen it all in his world. The phone rings, and the Brigade Leader rushes out. Elizabeth tells him that Central Records have returned no match for the Doctor. This confuses the Brigade Leader as Central Records have never failed him before. They both interrogate him.

Doctor Williams is informed of a minor leak in the drill head. Sutton questions her and is frustrated when neither she nor the Director seem to be bothered. An alarm goes off.

Hearing the alarm, the Brigade Leader and Elizabeth rush out. The Doctor calls over the guard and immobilises him with karate.

Smoke and green goo are pouring out of the drill head. The Brigade Leader is ordering all of his men and all of the scientists to remain at their posts. Amongst this chaos, the Doctor sneaks forward.

Sutton orders the scientists around, to no avail. Doctor Williams watches the reading increase. The scientists start to abandon their posts; the Brigade Leader threatens to shoot them. The Doctor has found a toolbox and is scrabbling around looking for a microcircuit. He is discovered by Platoon Under Leader Benton, who holds a gun to his head and remarks there is a firing squad outside waiting. The Doctor implores with him, saying that he knows how to stop all this. Benton is unmoved and asks him "Are you coming with me quietly, or do I shoot you here and now?"

Episode 4
Elizabeth stops Benton. The Doctor thanks her, but she says that she only did so because it goes against procedure. The Doctor tries to buy time to fix the computer, and eventually Elizabeth allows it. The computer begins to work and assesses the problems. The Director is angry that the Doctor has been allowed access to the computer. Sutton and Elizabeth stick up for him.

Sutton and the Dictator argue about the safety precautions. Doctor Williams starts to listen to the Doctor's theories. The Doctor says that the heat and the pressure is proving too much for the velocity of the drill and that the only way to counteract it is to produce a reverse vortex by reversing all the systems. Reluctantly the Director agrees, then sends the Doctor away. Elizabeth compliments the Doctor, and then asks where he came from. He repeats his story about the parallel universe. She asks about the version of herself in the Doctor's universe. He says that she is a scientist. Elizabeth says that there is no similarity. The Doctor asks if she every contemplated being a scientist, and she admits she studied physics at university. The Doctor points out that it is there where the two points diverged. Elizabeth is doubtful, but the Doctor encourages her to think for herself.

Doctor Williams and Sutton talk about the Doctor and his motivations for saving them. Sutton says he intends on cutting the drill down to minimum speed, regardless of what the Director thinks. Doctor Williams tells Sutton that he needs to start towing the line a little more. Sutton refuses, despite knowing that those that disobey orders "disappear".

Elizabeth is told that the emergency is over, thanks to the Doctor. The Doctor warns Elizabeth about the dangers of the drilling operation.

The Director asks Sutton for progress and is told all is well. The Director tells Sutton he intends on increasing the drilling speed. Sutton says that this is madness. The Director threatens to dispose of Sutton if he continues to disobey him.

The Brigade Leader and Elizabeth are firing questions at the Doctor. They ask him his name, who sent him, whether he is a saboteur, what organisation he works for, whether he is a traitor, how he gained access to the complex, who helped him and which of their enemies he is working with. The Doctor does not answer. Elizabeth warns him they have other methods of extracting this information and repeats the question. The Doctor says that he came on his own, by accident, and has slipped sideways through time. Elizabeth asks the Brigade Leader for permission to go to stage two interrogation. He blocks this, as he is fearful the Doctor will die before talking.

The Doctor hears the acceleration of the drilling and rises to try to stop it. The interrogation continues. The Director enters, wanting to know what progress is being made. The Doctor draws attention to the Director's gloves and challenges him to take them off. The Director tries to brush over this, but the Brigade Leader asks him to. He does so, and his hands are bandaged underneath. He says that he scorched them. The Doctor begins babbling about the green goo and infection. The Brigade Leader orders the Doctor to be taken to the Security Centre and asks Elizabeth to supervise him into his cell. When they are alone, the Brigade Leader questions why the Director is so concerned about the Doctor. The pair squabble, and the Director leaves, saying he wants the Doctor "liquidated" by the end of the day.

Sutton and Doctor Williams conspire about the Director. Sutton is questioning why he is continuing to up the speed of drilling. Doctor Williams appears convinced by Sutton.

The Doctor is escorted to his cell by Platoon Under Leader Benton. He notices he has a sleeping figure in the cell next to him. Platoon Under Leader Benton says he will be sleeping for some time, as he has been shot with a tranquilliser dart. Elizabeth comes to check on him. The Doctor refuses to be interrogated any more, until Platoon Under Leader Benton orders him to his feet at gun point. Again, Elizabeth asks who the Doctor is and how he came to the complex. The Doctor, again, tells the truth. Platoon Under Leader Benton asks for a moment alone with the Doctor to extract the information from him. Elizabeth sends all the guards away. She puts to him that he is a protester from a free speech group who is forming a demonstration and that if he confesses to that he will only get a few years in a labour camp. The Doctor refuses. Elizabeth says she will leave him to the Brigade Leader and leaves. Left alone, the Doctor tries to talk to the sleeping figure. After no response, he goes to sleep. A green hairy hand emerges from beneath the sheets.

Back in the Doctor's universe, the Brigadier tells Liz that the UNIT soldiers have searched the entire complex for the Doctor, to no avail. They will not extend their search beyond the complex. Liz is concerned that the Doctor could be anywhere in space or time. When the Brigadier says that the Doctor can look after himself, Liz warns that he is not indestructible.

Sir Keith asks the Professor if there are any problems or precautions with the drilling. He responds in the negative to both. Sir Keith says he is going to London and, unless he receives some kind of assurances, he will tell the minister of the unsafe practices being carried about by the Professor. The Professor says he has no intention of playing it safe. When the Professor leaves, Sir Keith tells the Brigadier and Liz that he is not sure that the Minister will even listen, as he has been blinded by the Professor's promises of free energy. Sir Keith has an ominous feeling about the whole thing.

In the parallel universe, the Doctor awakens to snarling from the sleeping figure. He calls for the guard, who enters to investigate. He is attacked and killed by the animalised human under the sheet. The creature approaches the Doctor and bends the bars to enter the Doctor's cell. The Doctor flips his mattress onto the creature, knocking him over. The Doctor escapes, locking the door behind him. He runs into the complex and approaches a Land Rover. He is surrounded by people and in an effort to hide gets into the back of the truck as it drives off.

The drill is thirty five minutes from the centre of the Earth. Sutton asks Doctor Williams if everything is ready. Sutton has an ominous feeling about the whole thing and thinks they should be paying more attention to the computer.

The Doctor has found a pile of full radioactive protective suits in the back of the truck.

A guard discovers the carnage in the cell.

The truck draws up and the Doctor, now dressed in one of the suits, finds both soldiers and scientists waiting at the back of the vehicle. The Doctor starts handing out the protective suits to the men.

The drill is three minutes from the centre of the Earth. The Director stares intently at the readings.

The Doctor re-enters the compound with other similarly dressed men.

The drill is two minutes from the centre of the Earth. The disaster crew is at action stations. The Doctor and the other similarly dressed men enter the main area and line up. The Doctor sneaks away and begins to tamper with a computer. The drill is one minute from the centre of the Earth. The Brigade Leader notices the Doctor and calls to him. The Doctor unveils himself and shouts that the countdown should be stopped. The Director orders the Doctor to be shot. The Brigade Leader draws his gun. Sutton protests. The Doctor warns that they are about to release forces that they've never dreamed of. The drill lets out a high pitched whine. The Doctor angrily yells "Listen to that! That's the sound of this planet screaming out its rage!". Sutton attacks the Brigade Leader and implores the Doctor to run. Wherever the Doctor turns he is blocked by resistance security forces. The Director now has the Brigade Leader's gun and is pointing it at the Doctor. The countdown reaches zero.

Episode 5
The ground beneath them shakes, and they all fall to the ground. Everyone around them screams and abandons their posts in panic. The Brigade Leader attempts to stop them. The Doctor staggers to his feet and tries to stop Sutton from going in. The Director is attempting to as well. The Doctor questions that it seems that the Director is not feeling the heat quite as much.

Doctor Williams confirms that nothing can be controlled remotely.

Inside the drilling station, there is a huge explosion, and the green goo bubbles out of the drill.

Sutton and the Doctor enter in their protective suits. Sutton is struck about the head by the Director. Whilst Sutton is unconscious, the Director removes his helmet. The Director and the Doctor have a fist fight. The Director is winning when Sutton staggers to his feet and strikes the Director over the with a metal pole before collapsing in the fumes. The Doctor helps Sutton out. When the Doctor tells everyone what the Director did, they want to go in there and save him. The Doctor comments that he seems to like it in there. Sutton and the Doctor prepare to go back in when the door is closed from the inside.

Inside, the Director is purposely contaminating people with the goo.

The Doctor asks how thick the door is. Sutton replies that it is enough to stop a nuclear explosion. The Doctor warns that it will not be enough.

An explosion rocks the complex.

The Brigade Leader returns to see almost everybody has abandoned their post. Doctor Williams says that the computer is broken. The Brigade Leader reports of seismic tremors and earthquakes all over the country. The government have put him in control. Sutton asks if they have any plans to seal the shaft. The Brigade Leader says they do not. Sutton asks the Doctor if it is possible. The Doctor says that no substance in the world is strong enough to withstand the unleashed energy. The pressure will only get worse until, in days or weeks, the Earth will dissolve. An animalised human has appeared behind them. The Brigade Leader goes to attack it, against the wishes of the Doctor. The Brigade Leader tries to shoot it, to no avail. The Doctor uses a fire extinguisher, which immediately kills it. The Doctor explains that the creatures can't stand the cold. Sutton wants to leave. Doctor Williams says she will accompany him. The Brigade Leader draws his gun on them. Benton says he has found some resistance security forces. The Brigade Leader tells him to ensure nobody leaves the building.

Benton marshals his troops.

Doctor Williams is attempting to fix the computer. Sutton says there is no point and that they are all going to die. Doctor Williams says the whole complex needs re-wiring. Sutton says there is no chance of that as the government has abandoned them. Sutton softens his tone when he sees how distressed Doctor Williams is. She now realises that it is the end. She and Sutton embrace. Sutton says he plans to leave and asks if she wants to come with him.

Elizabeth is losing her mind at the planet's imminent demise. The Doctor says they still have a chance to save the other world. The Brigade Leader is exasperated that the Doctor is still continuing with that story. The Doctor explains the concept of the TARDIS and the fact he could use their nuclear reactor to get it working. He explains that in his world the drilling is behind schedule, and he can stop it before it takes place. The Brigade Leader wants to take a look at the TARDIS. As they leave, Doctor Williams tells him that all systems are breaking down. Once left alone, Sutton and Doctor Williams talk about when to escape.

The Brigade Leader inspects the TARDIS console. The Doctor shows a few movements left over from residual energy. The Brigade Leader still doesn't believe. Elizabeth asks to see some proof. The Doctor drains the storage unit to travel a few seconds into the future. He asks if the Brigade Leader is satisfied. He asks if the Doctor can take anyone else with him. The Doctor says he cannot, as it will create a dimensional paradox that will shatter the space time continuum.

Platoon Under Leader Benton is still keeping the resistance security forces in line despite the explosions around them.

As Doctor Williams is working, a voice calls to her over the tannoy. She finds Sutton, who hears it too. The Brigade Leader, Elizabeth and the Doctor join them to hear the voice of the Director asking Doctor Williams to raise the heat shield as the manual controls are jammed. Doctor Williams goes to do this. The Doctor tries to stop her, but the Brigade Leader draws his gun and allows her to do so. The heat shield opens halfway, and a figure in a protective suit pulls it the rest of the way. He pulls off the helmet to reveal the animalised human. He is joined by a group of others like him. They are not attacking, as they are acclimatising to the change in heat. Everyone tries to escape, but they are stopped by the creatures. Platoon Under Leader Benton enters and is immediately seized by the creatures. One of them rubs a handful of green goo across Benton's face, and he screams before falling to the ground. The Doctor pulls some wires out of the computer, and the door closes. This creates a distraction to allow them to escape into the office. Sutton wants to save Platoon Under Leader Benton, but the Doctor forbids it. Platoon Under Leader Benton staggers around in pain as he begins to turn into one of the creatures.

Sutton is dismayed that he was not allowed to save Platoon Under Leader Benton. The Doctor says that nothing could have been done as the heat would have sped up has change into one of the creatures; that is why he closed the heat shield. The Brigade Leader and Elizabeth tell Doctor Williams about the Doctor's "spacecraft".

In the Doctor's original universe, Sir Keith is on the way back from the ministry when he notices he is being taken a different route. The driver informs him that there is traffic. Sir Keith tries the car phone. It is not working. Sir Keith tells the driver that the minister has suspended the drilling pending a full review. Sir Keith begins to get suspicious of the driver, and he eventually confesses that the Professor ordered him to take the long route home and pretend to break down. Sir Keith asks the driver to return to the complex. As he does the pair are involved in a car accident.

In the parallel universe, the creatures are clawing at the office door.

Inside they are all discussing the revelations about the Doctor. They all believe him, with the exception of the Brigade Leader. The Doctor says he has a plan to get out of the office but is interrupted by one of the creatures breaking through the glass in the door.

Episode 6
The Doctor uses a fire extinguisher to push the animalised humans back. The Doctor needs ten minutes to execute his plan to connect the TARDIS to the nuclear reactor. Doctor Williams questions if there is any power running through the system. The Doctor checks the air conditioning system — it is working. Doctor Williams says it must have been switched to robot control; she would need to boost the output by resetting the emergency control, but the master switch in the next room needs to be fixed first. Sutton suddenly remembers that there is a huge amount of coolant in the adjacent room which they can use to hold off the creatures. The creatures break through, and they immediately put the plan into action. The Brigade Leader holds back the creatures with the fire extinguisher, while Sutton tries to access the coolant. The hose to the coolant has seized up, and the Doctor has to help. The Brigade Leader is surrounded, and his fire extinguisher has dried up. Just in time, Sutton has the coolant working and forces the creatures back. Sutton and the Doctor decide to stay and fix the master switch.

Once outside, the Brigade Leader wants to abandon the Doctor and Sutton. Elizabeth and Doctor Williams say they intend to stay.

The Doctor tells Sutton that he can go if he wants, but he refuses. Sutton asks the Doctor how he will convince them to stop drilling in his own universe. The Doctor says he may be able to convince Sir Keith. Sutton says he is dead, and the Doctor says he may still be alive in his own universe.

Back in the Doctor's original universe, the Brigadier receives a phone call saying that Sir Keith has disappeared. Benton enters and says that the Professor is refusing to see the Brigadier and has insulted him. The Brigadier loses his temper with Benton and tells him to tell the Professor he doesn't have a choice.

Liz is in the Doctor's hut, flicking switches to attempt to return the Doctor to his original timeline. The door rattles. Liz checks who it is and opens the door to reveal Sutton. He is curious what has happened to the Doctor, seeing as nobody saw him leave. He thinks that the Doctor blew himself up and that everyone is covering it up. Liz explains that there was some kind of accident but won't be drawn on any other details. Sutton tells Liz about Sir Keith.

The Professor rails against the Brigadier. The Brigadier tells the Professor of the disappearance of Sir Keith. The Professor suggests an accident. The Brigadier says there has been no report of an accident. The Professor suggests that he might not have heard what he wanted to hear from the minister and may have taken himself off. The Brigadier says that, due to not having heard from the minister, he thinks that penetration zero should be delayed due to Sir Keith's objections. The Professor refuses.

In the parallel universe, Sutton is still holding off the animalised humans. The Doctor has fixed the master switch. Sutton clears a path with the coolant, and they both escape, grabbing fire extinguishers as they go.

Doctor Williams sees the Doctor and Sutton emerge. They all run off.

Soon Bessie pulls up at the Control Centre. Doctor Williams immediately sets about fixing the computer. The Doctor and Sutton set off to get tools and cable. As they do, they feel the tremors of a distant earthquake. They head off to Bessie.

The animalised humans start emerging from the complex due to the fact it is warm enough outside for them now.

The Brigade Leader loses his temper at Doctor Williams, telling her to hurry up. Doctor Williams informs him that his shouting at her isn't helping. Elizabeth sides with Doctor Williams. The Brigade Leader explains that he has no intention of letting the Doctor escape alone.

The complex is now covered with the animalised humans.

The Doctor and Sutton have got back to the hut. Sutton is underwhelmed by the console. The Doctor asks him to fix the connector to the cable. Sutton warns him that if the entire output of the nuclear reactor is run through the cable, it will only last a few seconds. The Doctor assures him that that is all he will need.

The Brigade Leader asks Doctor Williams how much longer she will be. She says that there is a problem with the relay circuits, and she is attempting a double bypass. The Brigade Leader loses his temper again. Elizabeth turns on him. The Brigade Leader says he plans to hijack the TARDIS, and if the Doctor refuses to be persuaded, he will kill him.

Sutton implores the Doctor to make sure he stops them from drilling and connects the cable. He says that, with luck, it should work. The Doctor says they don't need luck but skill.

Doctor Williams thinks she is ready. She pulls the lever and nothing happens. She says there must be a fault. The Brigade Leader is furious for her wasting their time. She says she will try again, but it will involve re-wiring the whole system.

Sutton and the Doctor are waiting for the circuit to be complete. Sutton says that, if those explosions reach the nuclear reactor, they are all done for.

The Brigade Leader watches the shaft split open. The animalised Director enters. Doctor Williams and Elizabeth run out. The Brigade Leader shoots the animalised Director repeatedly until he falls to the ground. All three of them run off, pursued by the creatures. They are sporadically thrown to the ground by earthquakes.

Back at the hut, Sutton is impatient, but the Doctor is resigned to the plan having not worked. Sutton sees the trio coming. Doctor Williams apologises for the plan not having worked. The Doctor says it is fine. The Brigade Leader is furious and says it is far from fine. Sutton and the Brigade Leader argue. The Brigade Leader pulls his gun on him. Sutton says he will be only speeding up his death. The Brigade Leader pulls the trigger, but there are no bullets in the gun. The pair fight. The Doctor makes them stop, saying that they don't want to end their lives fighting like animals. They notice that Doctor Williams has gone back to the Control Centre to try to remedy the situation. Sutton goes to help her.

Doctor Williams is re-wiring the computer when Sutton enters, furious. She asks what any risk to herself matters. The animalised Director awakes, and Sutton attacks it with a fire extinguisher. As he does, Doctor Williams gets the circuit working. They run to the hut.

Elizabeth notices that the console is working. The Doctor says it is gaining power rapidly. The Brigade Leader pulls his gun and orders him to take them with him. He fires the gun in the air to prove it is now loaded. The Doctor says he wants to, but can't as it will cause a cosmic disaster. The Doctor says the Brigade Leader is going to have to shoot him. There is a gunshot, and the Brigade Leader falls. Elizabeth re-holsters her revolver; she is the one who fired the shot. The other three implore the Doctor to leave now.

A huge explosion shakes the complex. Lava begins to flow from where the drill shaft was. Men and animalised humans run in terror.

The Doctor says he cannot dematerialise as the power is too erratic. Lava begins to flow towards the door of the hut.

Episode 7
The Doctor is prostrate and unconscious on the floor of the hut. He is discovered by Liz, who calls for Benton to fetch the Brigadier.

It is three hours and twenty two minutes until the drill penetrates the Earth's crust. The Professor gives orders to boost the drilling. Petra is unsure as to the safety, but the Professor orders it. Petra tells Sutton, who wants to confront the Professor, but Petra stops him, saying that she will try first.

Benton tells the Brigadier about the return of the Doctor. Sutton overhears.

The Professor will not listen to Petra. He is strongly affected by a noise that emerges from the drill. Petra is worried for his health, but he says he merely has a headache. Sutton tries to persuade the Professor. Again he is blocked, and again the noise has an effect on the Professor. The Professor storms off, leaving Petra and Sutton worried about his mental health.

Liz is checking the Doctor's health. All is fine, and he is just in some kind of coma. The Brigadier wants to fetch a doctor, but Liz blocks him.

Sutton warns the Professor of an issue with the number two output pipe. The Professor ignores him. Sutton loses his temper, and the Professor says that if he is so worried, he should leave. Sutton goes to leave when Petra stops him. Sutton tries to convince her to come with him, but she says she can't. They are interrupted by an explosion from the drill head.

The Brigadier is informed of the issue. The Doctor stirs. He mutters that the number two output pipe has blown. The Brigadier is stunned, as he has only just heard that information himself. Still in his coma, the Doctor mutters, "Reverse all systems immediately", before slipping back into unconsciousness. Liz goes to Central Command to tell them what the Doctor said.

The Professor is struggling to keep everyone in their positions and is refusing to stop the drilling. Liz enters and asks Sutton and Petra what would happen if they reversed the systems. Sutton says it is not a bad idea. Petra says they would never get the Professor to agree. Liz says they should just do it. They all rush off.

The Doctor stirs in his coma.

It has worked. Liz says it was the Doctor's idea.

The Professor is angry at Petra for having not run the plan past him.

The Doctor awakens to the Brigadier and Liz. He tells the Brigadier he looks better with a moustache. He checks his pulse and is healthy. He tells Liz and the Brigadier where he has been. They think he is still delirious. He asks the Brigadier, who he calls the Brigade Leader, if they have caught the animalised scientist, whether the Professor seems ill and the state of the drilling. There is a knocking at the door. It is Sir Keith, who explains about his forced delay and the car accident. The Doctor is overjoyed to see he has survived his accident. Sir Keith tells the Brigadier that the Professor is going to face some serious charges. The Doctor has realised that with an infinity of universes comes an infinity of choices, free will is not an illusion and patterns can be changed. The Doctor stops the Brigadier from calling a doctor for him and tells Sir Keith what is going to happen.

The Doctor bursts into Central Command and says that drilling must be stopped. The Professor orders the Brigadier to arrest him. The Doctor rushes to a computer and attacks it with a wrench. The Brigadier pulls him away and orders him to be taken to the sick bay. Sir Keith confronts the Professor. The Professor says he has no intention of going to see the minister until after drilling is complete.

Petra tells the Professor that they will be switching to robot controls in forty nine minutes. The Professor says he feels cold and orders her to increase the temperature. He has some kind of fit that causes the scientists to look at him in shock. He orders them all to leave the area as he will finish the procedure alone.

Sutton and Petra are shocked as to what the Professor is doing. The Professor closes the heat shield.

The Doctor uses Venusian karate to knock out his guards before running off and hiding. The guards come to and run past him in his hiding place. The Doctor is approached by the animalised scientist. He neutralises him with a fire extinguisher.

The Professor studies the green goo that is dripping out of the drill head. He rubs his hands and face with it before falling to the ground.

Petra hears the cries of the Professor through the tannoy and is concerned for the Doctor. Sutton tells Sir Keith that they cannot access him as he has locked the heat shield from the inside.

Behind the heat shield, the Professor is fully animalised.

The computer is advising that the drilling should be stopped. The Doctor re-enters just as the heat shield rises and the animalised Professor emerges. The Professor attacks the Doctor with a chair, but he and Sutton blast him with fire extinguishers, killing him instantly. The Doctor orders that the drilling be stopped. Sutton says that they should cut off the power. Petra warns that this would cause the drill to disintegrate; Sutton says that would be for the best. Petra stops the drilling, but it continues. Sir Keith warns of the buffer controls, which cause the drill to slow rather than stop dead. This means the drilling will continue for five minutes — long enough for the drill to penetrate the Earth's crust. The Doctor and Sutton run off and discover the server switches have been smashed. With one minute left, the Doctor begins to tamper with the switch. Everyone looks on, worried. With thirty-five seconds left, the Doctor and Sutton return, having stopped the drilling for good. Liz hugs the Doctor. The Doctor says the shaft should be filled in immediately, while the Brigadier arranges for a stretcher party to take away the Professor's body.

Back in the hut, the Doctor and Liz are working on the TARDIS console. There is a knocking at the door. It is Sir Keith, accompanied by the Brigadier. He has come to say goodbye. Sir Keith says everyone is leaving as the project has been abandoned. The Doctor is told that he has one more day with the nuclear reactor before it is dismantled. Sir Keith also informs them all that Sutton and Petra left together. Once alone, Liz and the Brigadier ask why the Doctor still wants to use the nuclear reactor. The Doctor says that the console is now fully functional, and he can use it at will. The Brigadier scoffs at him, and the Doctor says he reminds him of the Brigade Leader. He bids goodbye to Liz before saying that he cannot stand another moment with the Brigadier, whom he describes as a "pompous, self-opinionated idiot". He flicks a few switches and disappears with the console; this time, Bessie remains in the hut. Liz turns to the Brigadier, cross that he has forced the Doctor to leave. There is a cough at the door. A rather bedraggled looking Doctor stands at the door. He informs them he moved a few seconds forward in time and space, landing in the rubbish tip! The Doctor tries to smooth over his cross words to the Brigadier in an effort to get some UNIT soldiers to return his console, which has landed in a somewhat inaccessible position. Liz laughs.

Cast

 * Dr. Who — Jon Pertwee
 * Liz Shaw / Section Leader Elizabeth Shaw — Caroline John
 * Brigadier Lethbridge-Stewart / Brigade Leader Lethbridge-Stewart — Nicholas Courtney
 * Sergeant Benton / Platoon Under Leader Benton — John Levene
 * Professor Stahlman / Director Stahlman - Olaf Pooley
 * Sir Keith Gold — Christopher Benjamin
 * Petra Williams / Dr Williams - Sheila Dunn
 * Greg Sutton / Greg Sutton - Derek Newark
 * Private Latimer - David Simeon
 * Private Wyatt - Derek Ware
 * Harry Slocum - Walter Randall
 * Bromley - Ian Fairbairn
 * RSF Sentry - Roy Scammell
 * Patterson - Keith James
 * Primords - Dave Carter, Pat Gorman, Walter Henry, Philip Ryan, Peter Thompson

Uncredited cast

 * Technicians - Colin James, Steve Tierney (DWM 305)

Crew

 * Writer - Don Houghton
 * Action / Stuntwork - HAVOC
 * Assistant Floor Manager - Sue Hedden
 * Costumes - Christine Rawlins
 * Designer - Jeremy Davies
 * Film Cameraman - Fred Hamilton
 * Film Editor - Martyn Day
 * Film Sound - Graham Hare
 * Make-Up - Marion Richards
 * Production Assistant - Chris D'Oyly-John
 * Script Editor - Terrance Dicks
 * Special Sounds - Brian Hodgson
 * Studio Lighting - John Green
 * Studio Sound - John Staple
 * Theme Arrangement - Delia Derbyshire
 * Title Music - Ron Grainer
 * Visual Effects - Len Hutton
 * Producer - Barry Letts
 * Director - Douglas Camfield

Uncredited crew

 * Effects Assistant - Peter Logan, Ian Scoones (INFO: Inferno)
 * Floor Assistant - Frank Mullan (INFO: Inferno)
 * Make-Up Assistants - Judy Cain, Sue Duckworth, Irene Walls (INFO: Inferno)
 * Design Construction Organiser - Colin Bowles (INFO: Inferno)
 * Producer's Secretary - Sandra Brenholz (INFO: Inferno)
 * Technical Managers - Ray Hider, Lance Wood (INFO: Inferno)
 * Film Sound Assistant - Jack Curtis (INFO: Inferno)
 * Director's Assistant - Sue Upton (INFO: Inferno)
 * Film Camera Assistant - Hugh Miles (INFO: Inferno)
 * Grams - Tony Philpott, Gerry Borrows (INFO: Inferno)
 * Costume Assistants - Terry Styles, Pat Trigger (INFO: Inferno)
 * Vision Mixer - John Gorman (INFO: Inferno)
 * Lighting Cameraman - Mike Wilson (INFO: Inferno)

Locations

 * Sutton was flown in from Kuwait.

Individuals

 * The Doctor met King Edward VII in Paris.
 * The Doctor states he was at Krakatoa during the eruption of 1883.
 * Latimer is one of the soldiers in the other universe.
 * Phillips is working on the Inferno project.

TARDIS

 * The Doctor has removed the console unit from the TARDIS and is running experiments with it. It is also demonstrated that the console itself can travel through space-time without the need of an outer shell, but requires an external power source to achieve transit.

Story notes

 * This story had the working titles of The Mo-Hole Project, Operation: Mole-Bore, The Mole-Bore and Project Inferno.
 * This is the only season finale in the Third Doctor era to not be written by Robert Sloman.
 * The primordial mutant creatures are named "Primords" in the closing credits of episodes five and six and publicity material, but are left unnamed in the story's dialogue.
 * The opening credits for this serial were unique in that after the initial titles, the name and part number of the serial were superimposed on footage of a lava flow, with no music. Unique episode title cards were an occasional fixture of classic series episodes during the 60s (e.g. TV: The War Machines, The War Games). Inferno would be the final story in the classic series to feature a unique title card. The practice would be briefly revived, albeit in the form of unique logos for the show title itself, in the Autumn 2012 half of BBC Wales' Series 7.
 * The footage of a volcano erupting used for these title cards was also used in The Enemy of the World and The Time Monster.
 * The Radio Times programme listing for episode one was accompanied by a black and white rehearsal shot of the Doctor standing at the TARDIS console, with the accompanying caption "Knock, knock. Who's there? 5.15", while that for episode seven was accompanied by a black and white photograph of the mutated Director Stahlman, with the accompanying caption "Meeting the Primord. Dr. Who: 5.25".
 * In spite of Douglas Camfield receiving sole credit as director, the second studio recording block and studio blocks 3 and 4 were directed by producer Barry Letts after Camfield had a minor heart attack on 27 April 1970. Letts later stated that Camfield's preparations for episode three's studio recording were so meticulous that he just followed Camfield's existing camera script. For the other episodes, Letts worked to his own plans, which he had to hurriedly construct. In the end, Camfield directed all the location filming and designed the direction executed by Letts on episode three's studio recording. Nevertheless, Camfield remained credited as director, as BBC regulations at the time forbade the same person being credited as producer and director.
 * Derek Ware did not perform the scene where the mutated RSF Private Wyatt is shot and falls to his death from the top of one of the cooling towers, in case he was injured, as he was also needed for studio recording. His place was taken by Roy Scammell who, curiously, also played the RSF sentry who fires the fatal shot. Ware stated in an interview that Scammell had already signed the contract to do the fall before Ware had been cast as Wyatt.
 * The role of Petra was given to Sheila Dunn (Douglas Camfield's wife) after Kate O'Mara was not available to play the part. O'Mara was, years later, cast as, a renegade Time Lord.
 * Episode six has a small damaged section on the tape, which the Doctor Who Restoration Team replaced by painstakingly recolouring the appropriate section of the existing 16mm black & white film telerecordings.
 * Caroline John enjoyed her role as Section Leader Elizabeth Shaw and said that it was fun playing "baddie" Liz. She also says she hated doing the scenes when she was playing the "goodie" version because it was boring compared to being an evil character. She was particularly upset though about the scene in which Shaw shoots Brigade Leader Lethbridge-Stewart, as she was pregnant at the time. As a result, the scene was recorded with the weapon fired from out-of-shot, after which Shaw was shown returning the gun to her holster.
 * Nicholas Courtney has also said he enjoyed playing the parallel version of the Brigadier. He called it his "favourite" in an interview with Doctor Who Magazine in 2009. The DWM staff remembered this by including it in his tribute issue as that month's "The Fact of Fiction".
 * At Doctor Who fan events, Courtney frequently recounted an incident which occurred during shooting of the scene with the revelation of the Brigade Leader and his eye patch. The scene begins with Courtney having his back to the camera (and to all the other actors) before spinning around in his swivel chair to reveal the Brigade Leader's visage and eye patch. When the scene was shot, Courtney spun around to discover that all the other actors and crew members were also wearing eye patches. According to the story, he then proceeded to perform the entire scene as if nothing unusual had occurred. The "eye patch story" became so closely associated with Courtney that Steven Moffat wrote scenes in which "everybody was wearing an eye patch" into the 2011 episode The Wedding of River Song as a tribute to Courtney, who had died earlier that year. (DWMSE 31)
 * During the scenes set on the parallel Earth, images (supposedly) of the UK's dictatorial leader are seen on posters. The image used is that of visual effects designer Jack Kine, in homage to the 1954 BBC adaptation of George Orwell's where the face of Big Brother was Head of Television Design Roy Oxley (Kine had worked on the visual effects for that production).
 * Inferno marks the first story in Doctor Who to be set in a parallel universe.
 * The scenes on top of the nuclear reactor in episode two were not easy for Jon Pertwee, as he was afraid of heights. It took him fifteen minutes just to summon up the confidence to film the scene.
 * In episode three, during the chase scene on the parallel Earth, Bessie's bumper gashed open stuntman Alan Chuntz's leg as it passed as he jumped out of the way a fraction later than he was supposed to. The gash was so severe that he had to go to A&E. John Levene stated on the DVD commentary that "it was the worst wound [he]'d ever seen" and after Pertwee saw the wound and learned he caused it, he became sick and almost couldn't carry on filming until a few hours later. Pertwee even went as far as buying Chuntz's wife a gift to apologise for the accident.
 * Olaf Pooley initially refused to put on the Primord costume but eventually Barry Letts persuaded him to do it and he was later glad that he did agree to wear it.
 * A Doctor Who Unbound story later touched on a narrative element of this story. According to Sympathy for the Devil — a narrative set in a different parallel universe — research into the possibilities of Stahlman's gas was still ongoing in 1997, the year that the Doctor in that universe's exile on Earth began.
 * This was the final story to feature the original TARDIS console prop. Having been in use since the show's first episode in 1963, the prop had gradually deteriorated over the years, with numerous bits and pieces falling off or being replaced. After this story aired, the prop was deemed unusable and junked. For the TARDIS console unit's next appearance in The Claws of Axos, a new prop, designed by Kenneth Sharp, was built.
 * This was the last televised story to use stock music in lieu of an original incidental music score. Notably, all of the stock pieces used were composed by Doctor Who theme arranger Delia Derbyshire, making this the nearest she came to actually scoring an episode of the show.
 * As well as the obvious uniform differences, the RSF soldiers are wearing Wehrmacht-pattern equipment belts and carry WW2-style wooden rifles with bayonets fixed rather than the more modern L1A1s used by UNIT.

Ratings

 * Episode 1 - 5.7 million viewers
 * Episode 2 - 5.9 million viewers
 * Episode 3 - 4.8 million viewers
 * Episode 4 - 6.0 million viewers
 * Episode 5 - 5.4 million viewers
 * Episode 6 - 5.7 million viewers
 * Episode 7 - 5.5 million viewers

Myths

 * The parallel universe aspect of the story was added to the scripts at the production team's suggestion to ensure that there was sufficient material to fill seven episodes. (Though Terrance Dicks has claimed this in several documentaries, the parallel universe aspect was present as far back as Don Houghton's original story outline. It actually appears to have been the Primords who were added at the production team's suggestion.)
 * This was Caroline John's last story as Liz as she was pregnant and could not return for the following season. (Although it is true that the actress was pregnant, Barry Letts was unaware of this when he decided against renewing her contract.)

Filming locations

 * Kingsnorth Industrial Estate (formerly Berry Wiggins and Co Ltd), Hoo St Werburgh, Kent
 * Ealing Television Film Studios, Ealing Green, Ealing
 * BBC Television Centre, Shepherd's Bush, London

Production errors

 * On the Nuclear Output Gauge in the Doctor's workshop, Mega-volts is spelled "Megga Volts".
 * In episode four, when the Doctor has been returned to the Brigade Leader's office, the door is shown to be open. The camera then focuses on the Brigade Leader and when it returns to the Doctor and Benton, the door is now closed.
 * During some shots of episode six when Sutton is holding off the Primords with coolant from a fire extinguisher, none is actually coming out of the nozzle.
 * In episode seven, the dead Primord Stahlman has a little bit of human skin poking out of his neck.
 * Director Stahlman is seen to wear a nameplate that reads STAHLMANN, but he is actually credited on-screen on "Director Stahlman".
 * In episode seven, while the Doctor is stopping the drill, Caroline John's floor-marker is clearly visible.
 * The countdown announcements are read out every ten seconds. In the final episode, the last one heard before the Doctor and Sutton stop the drill is 'zero minus fifty seconds'; therefore the timer should have been, approximately, forty-five seconds but the announcement afterwards declares that the drill was stopped at 'zero minus thirty-five seconds'.

Continuity

 * PROSE: Timewyrm: Revelation states that the dictator was one of the alternative regenerations the Time Lords offered to the Doctor in TV: The War Games.
 * Liz Shaw does not feature in any subsequent serials, although an illusory image of her is seen in TV: The Five Doctors. The circumstances surrounding her departure from UNIT are told in PROSE: The Scales of Injustice. In TV: Terror of the Autons, it is merely mentioned that Liz went back to Cambridge.
 * PROSE: Interference - Book One suggests that Stahlman's ooze is a result of the hole to the Spiral Yssgaroth at the centre of the Earth.
 * PROSE: The Face of the Enemy is a sequel to Inferno, revisiting the "alternate" world.
 * PROSE: Ashes of the Inferno is another sequel, dealing with the aftermath of the serial's events.
 * PROSE: Still Lives features a UNIT corporal who becomes affected by the events of this story.
 * The ooze's transformation of humans into Primords is paralleled with the Wyrm's creation of the Wyrm Callers in AUDIO: The Adolescence of Time.
 * The Fourth Doctor later encountered Marshmen, creatures that shared the Primords trait of being temporarily weakened by gas sprayed from a canister. However, unlike the Primords who were weakened by carbon dioxide in fire extinguisher spray, the Marshmen were weakened by oxygen from oxygen canisters. (TV: Full Circle)
 * In 2007, the Doctor travelled to another parallel universe in which there was a Republic of Great Britain. (TV: Rise of the Cybermen / The Age of Steel)
 * A sketch that washed up on the shores of Sumatra following the Krakatoa eruption was later shown to Rose Tyler, depicting the Ninth Doctor in front of a volcano. (TV: Rose)
 * Also during the Krakatoa eruption, the Xylok which became Mr Smith was unearthed. (TV: The Lost Boy)
 * Another great drilling project into the Earth's crust was started in the Welsh village of Cwmtaff in the year 2020. (TV: The Hungry Earth)
 * The Eleventh Doctor later sang "La donna è mobile", again with altered lyrics, while in the shower in TV: The Lodger.
 * In February 1970, the journalist James Stevens dismissed Greg Sutton's outlandish claim that a green slime from the centre of the Earth transformed scientists into wolf monsters during the Inferno Project. He described Sutton's story as sounding like the plot of a "science fiction potboiler". (PROSE: Who Killed Kennedy)
 * After the failure of the Inferno Project, among other incidents, was publicised by James Stevens in his "Bad Science" series of articles in the Daily Chronicle, Harold Wilson's position as Prime Minister of the United Kingdom became untenable and the Labour Party lost the general election in June 1970 to the Conservatives, led by Edward Heath. (PROSE: Who Killed Kennedy)
 * By 1973, Sutton had befriended the First Doctor's former companion Ian Chesterton. (PROSE: Byzantium!)
 * Jo Grant later mentioned the events of the Inferno Project in AUDIO: Gardeners' Worlds.
 * In a parallel universe in which the Doctor's exile on Earth did not begin until 1997, research into the possibilities of Stahlman's gas was still an ongoing project. (AUDIO: Sympathy for the Devil)

DVD releases
This story was released as Doctor Who: Inferno.

Released:
 * Region 2 - 19 June 2006
 * Region 4 - 6 July 2006
 * Region 1 - 5 September 2006

Contents:
 * Commentary by Nicholas Courtney, Barry Letts, Terrance Dicks and John Levene.
 * Can You Hear the Earth Scream? - A 35-minute documentary that looks at the making of Inferno. With contributions from Caroline John, Nicholas Courtney, John Levene, Ian Fairbairn, Barry Letts, Terrance Dicks and Derek Ware.
 * The UNIT Family (Part One) - A 36-minute documentary that looks at the role of UNIT in the world of Doctor Who through to the end of Jon Pertwee's first year as the Doctor.
 * Deleted Scene - A 2-minute scene cut from the original UK transmission of episode five, but which was retained for overseas screening.
 * Visual Effects Promo Film - An excerpt from a BBC Visual Effects Department showreel.
 * The Pertwee Years - Introduction - Jon Pertwee's original introduction to the final episode of this story.
 * Radio Times Billings - Articles and listings from Radio Times (DVD-ROM PC/Mac).
 * Doctor Who Annual 1971 (DVD-ROM).

Notes:
 * Editing for the DVD release was completed by the Doctor Who Restoration Team.

DVD special edition
Inferno has been re-released as a special edition in 2013.

Digital releases
This story is available:
 * for streaming through BritBox (US) as part of Season 7 of Classic Doctor Who.

Video release
This was released as a double-cassette pack on VHS in the UK in episodic format in March 1994, including in episode five the scene not shown on the original UK transmission (see DVD releases above).