The Entropy Plague was the one hundred and ninety-seventh story in Big Finish's monthly range. It was written by Jonathan Morris and featured Peter Davison as the Fifth Doctor, Sarah Sutton as Nyssa, Janet Fielding as Tegan Jovanka and Mark Strickson as Turlough.
It concluded a trilogy of the Fifth Doctor's return to E-Space that began in Mistfall. It marked the final chronological departure of Nyssa, after she sacrifices herself to allow her companions to return to N-Space.
A Great Darkness is spreading over E-Space. Entropy increases. In search of a last exit to anywhere, the TARDIS arrives on the power-less planet of Apollyon, where the scientist Pallister guards the only way out — a mysterious portal. But the portal needs power to open, and the only power Pallister can draw on is the energy contained within the molecular bonds of all living tissue...
The Doctor, Nyssa, Tegan and Turlough soon learn that neither Pallister nor his ally, the space pirate Captain Branarack, will stop at murder to ensure their escape. But they're not the only menace on Apollyon. The Sandmen are coming — creatures that live on the life force; that live on death.
Death is the only way out into N-Space. Death, or sacrifice.
But whose death?
Adric calls Neeka over the intercom to check up on her when he hears the TARDIS arrive and upon encountering the Doctor, learns that his mother Nyssa is gone forever, lost beyond the reach of the TARDIS in E-Space. Adric demands the Doctor explain what happened and why she will never return.
The Doctor, Nyssa and Turlough are chasing after Tegan who has been kidnapped by some space pirates from Isenfel. They crash-land on Apollyon where the TARDIS begins to lose power and they go out to explore and potentially find Tegan. They find a shanty town where they learn that the planet has no power and are celebrating "the end", saying that the stars are slowly going out and the end of the universe is closing in on them. Suddenly they spot a spaceship and suspecting Tegan to be aboard, chase after it. They see Tegan taken from the ship and follow her and her captors, Captain Branarack and his henchman. After bribing the robot guard, the Doctor, Turlough and Nyssa manage to enter and talk to Cherryanne, who explains that their friend is a tribute meant to be sacrificed and never to be seen again. They manage to free Cherryanne who explains how she and her brother ended up on Apollyon. The guard detects her escape and the Doctor distracts it to let her and Nyssa escape, while the Doctor requests the robot guard take him and Turlough to meet whoever is in charge. They are brought face-to-face with Pallister, a science tech who has created a laboratory entirely without power. He explains to an inquiring Turlough he is attempting to open a CVE and takes them to see the portal. He then gives Captain Branarack permission to pass through the portal, explaining that a "tribute" is required to provide energy from their molecular bonds almost like a human battery to power and stabilise the portal by being put it an induction chamber, allowing people to pass through it to N-Space. The Doctor, Turlough and Tegan are briefly reunited before Tegan is taken and seemingly sacrificed to allow Branarack's ship to pass through the portal to N-Space...
Tegan exits the TARDIS in the present and greets Adric while the Doctor explains to him that she and Turlough had been put into an induced sleep, then goes to check on Turlough and leaves Tegan to tell him what happened next.
Pallister's machine shuts down and the portal begins to destabilise, and they suspect the Doctor of sabotage. However, he makes a bargain saying he will help them discover what happened in exchange for Tegan's release. Pallister agrees. They descend to the lower depths but Tegan is then saved by a disguised Cherryanne in large armor and reunited with Nyssa, who created a temporary distraction. Tegan updates Nyssa on the Doctor's situation and the three of them decide it best to get away for now. Cherryanne takes them to her hideout where she had been taking care of her sick brother Raldarin. Cherryanne explains that he has the entropy plague, and warns them that they cannot touch him, saying that it may be transferred through contact. Nyssa explains that the CVE must be sucking the energy out of this system and notes how disease seems to cause people to take drastically dangerous actions like Pallister operating such a dangerous portal. She attempts to devise a plan to help the sick and the next day she and Tegan go to the market where she pawns off her last possession of Traken, a comb, in exchange for some food. However, for a few seconds they notice that organic decay is accelerated due to the use of the portal, and the food goes bad and they are unable to return it.
Just then they spot the Doctor and Pallister in a local tent and go over to talk with him. She demands an explanation from him and he reluctantly explains that Pallister is the only one who will be able to get them back to N-Space and hence his attempts to get "chummy" with him. Despite them reminding him that Pallister kills people to do it, the Doctor claims that E-Space is dying anyway and this seems to be their only chance and he can't always save everyone. The two reject this but he begs them to go back to the TARDIS and gives them the key, demanding they stay put until all this is over. He then hurries away. Tegan and Nyssa return to Cherryanne but they spot the sentinels and want to give themselves up to avoid Cherryanne putting herself in danger for their sake, however, she refuses and hides them despite their protests. When the sentinels leave after warning Cherryanne, Nyssa says she and Tegan will go back to the TARDIS to get food and medicine. However, they can't find the TARDIS, noticing it has been dragged to Pallister's citadel and decide to try find it but they hear people running away crying that the Sandmen are coming. Nyssa and Tegan attempt to escape them as they watch the Sandmen drain people's energy, killing them and leaving them as a pile of dust. They try to enter the citadel but the robot guard denies them access as it also denies access to the pleading citizens attempting to escape the Sandmen, deeming that they are too unhealthy, badly effected by entropy plague. The two manage to get away but are found by Cherryanne and they return back to her hiding place... only to find out that Raldarin has been turned into a Sandman as well...
Tegan, experiencing residual effects, becomes very tired and the Doctor helps her back into the TARDIS to rest and leaves a newly awakened Turlough to explain the rest.
He explains that The Doctor attempted to find the problem with Pallister's machine after he, Turlough and Pallister go to see the problem and fixes it, but when they return they find Tegan has escaped. The Doctor convinces Pallister that they didn't sabotage him nor help Tegan escape and while he reluctantly accepts, they are attacked by Captain Branarack who is furious at being unable to pass through the portal. They take Turlough as a tribute instead and put him in the induction chamber despite the Doctor's protest in order for Pallister to demonstrate to Captain Branarack that the machine works. They all suffer entropic acceleration, and when Branarack attempts mutiny Pallister has his sentinels easily subdue him, his weapons rendered useless by being aged to decaying, rusting metal and he and his crew pushed to their physical decay. Pallister has them locked up and wants the Doctor's help while Turlough faints, an after-effect of the induction chamber.
Turlough awakens and the Doctor tells him what he's been up to, including seeing Tegan and Nyssa and instructing them to hide in the TARDIS and explains that they need to close the CVE and by closing it E-Space will stop its immediate decay and have a few centuries left to give the inhabitants time to live out their natural lives so that no one has to die needlessly. He then tells Turlough that he will be sacrificing himself to send him, Nyssa and Tegan through the portal back to the safety of N-Space and will close the portal from this side, trapping himself in E-Space, despite Turlough's protests, also saying he has tricked Pallister. They are interrupted by Pallister who has had the TARDIS brought back at the Doctor's "request" (claiming it will help his machine with the CVE) and they discover that Nyssa and Tegan didn't listen to him as they are not inside the TARDIS and he guesses that they are with Cherryanne, and he asks some sentinels be sent out to find them. They follow Pallister to the holding cells which are crowded by people and hear Captain Branarack demand to be let out as one of his men has already caught the entropy plague. Pallister panics and has his remaining sentinels that have not been effected by the entropy drive all the prisoners, those effected by entropy plague and those not, out of the settlement. The Doctor warns him that this will only spread the plague faster but Pallister is adamant and refuses. Just then a sentinel informs them that people are attempting to get inside the citadel due to the outbreak of Sandmen caused by Pallister ordering the release. The Doctor convinces Pallister to close the portal to stop the entropy decay but only after Pallister himself and Turlough, Nyssa, Tegan and Cherryanne have passed through onboard Captain Branarack's ship, the Buccaneer. Tegan, Nyssa and Cherryanne are brought to them by the sentinels and the Doctor explains his plan, but they protest and Nyssa and the Doctor argue as Nyssa demands that he let her stay behind in his place since she can do the most good to help Apollyon recover once the portal is closed and things return to some semblance of normal...
The Doctor then gets in a heated argument with Turlough who says that they can sacrifice Captain Branarack and his crew instead, as he claims that their lives were less valuable which disgusts the Doctor. However, it is too late as Captain Branarack and his remaining crew find them and take them hostage, having overheard their situation. They decide to sacrifice Cherryanne for use in the induction chamber as revenge against the Doctor, to make him suffer, and force Pallister to give uncountermandable orders to his sentinels to kill anyone that tries to get in their way and thwart their plan. Captain Branarack brings Pallister onboard and has the sentinels prepare for their departure, leaving the Doctor, Nyssa, Turlough and Tegan to be trapped in E-Space. Just then the Sandmen, having managed to breach the citadel, descend upon the ship, destroying the sentinels in the process while Raldarin, in a last act of conscience, manages to stop the induction chamber from killing Cherryanne before losing the rest of his mind. The portal is forced open into a permanent state and Cherryanne sacrifices herself to stabilize it much to the parties regret. Thinking quickly, the Doctor manages to order the sentinels to get the TARDIS aboard the now nearly-destroyed Buccaneer, the entropy field having vaporized Branarack, Palliser and the crew before-hand. They reluctantly leave Cherryanne to seal the portal after she volunteers herself as a sacrifice to close it once they all get safely back to N-Space, however, they notice that the portal is still unstable. The Doctor realises he must go back and sacrifice himself to stabilise and close the portal, however when he attempts to leave the ship, he finds the door locked and sealed, and to his horror, realises that they have been locked in by Nyssa. They manage to contact her and the Doctor tries to persuade her to let him take her place, explaining that once sealed she will never be able to escape and they will never be able to come back for her. However, it is too late and the ship passes through the portal, leaving Nyssa behind and returning the Doctor, Tegan and Turlough to N-Space.
The Doctor then finishes the story, explaining to Adric that once they arrived back in N-Space, the TARDIS returned to life and Tegan and Turlough collapsed, effected by the residual effects after which the Doctor had put them into stasis to sleep in order to help them recover. He suspects that Nyssa is still alive even after using herself in the induction chamber to close the portal but they are unsure. Adric angrily tells the Doctor to leave, berating him for not doing anything to save his mother despite the Doctor's attempts to assure him that he did his best and didn't want this outcome either.
Nyssa recounts what happened to her after the portal closed in a letter addressed to Adric, how she helped the people of Apollyon through their sickness and recover and how in her final days she tends a garden as she has taught the people of Apollyon everything she can and she is now close to death. She expresses her thoughts, her love and her sorrows to Adric and his sister in the letter despite knowing full-well it will never reach him, explaining that she wanted to put her thoughts down before passing away but notes that a new star, never-before seen, was spotted in the sky a few nights ago, prompting her to claim that there may be a future yet for the universe of E-Space.
- The Doctor - Peter Davison
- Turlough - Mark Strickson
- Nyssa - Sarah Sutton
- Tegan - Janet Fielding
- Cherryanne - Catherine Skinner
- Pallister - Robert Duncan
- Branarack - John Voce
- Robot / Adric Traken - Alastair Mackenzie
- Raldarin / Sandmen - Chris Finney
- Apollyon's sun is a red giant.
- Tegan contemptuously refers to Captain Branarack as "an overdressed Neanderthal" and "Long John Silver."
- Adric once showed Nyssa how to pick locks.
- Cherryanne is two years younger than her brother Raldarin.
- The Doctor mentions Newton's first law.
- The Doctor tells the Robot guard "lead on, MacDuff", a line from Shakespeare's play Macbeth.
- The Doctor mentions Charles Babbage.
- The Doctor mentions that looking at the portal of the CVE was like looking down the side of Niagara Falls.
- Pallister exploits the energy in chemical bonds via magnetic induction to operate the portal and the CVE.
- The Doctor gives Tegan the TARDIS key.
- This story was recorded on 30 June and 1 July 2014 at The Moat Studios.
- Subscribers whose subscriptions included this story also received the audio short story String Theory.
- When the TARDIS is crash-landing on Apollyon, the cloister bells can be heard in the background.
- The Doctor notices the inhabitants of Apollyon carry momentos of the dead with them, which he explains is momento mori.
- The Doctor tells Adric Traken that the TARDIS accidentally travelled through a CVE to E-Space. (AUDIO: Mistfall)
- Adric Traken refers to his encounter with his mother Nyssa on Valderon one month earlier. (AUDIO: Prisoners of Fate)
- The Doctor refers to the fact that Tegan was kidnapped from Isenfel. (AUDIO: Equilibrium)
- Nyssa refers to the destruction of Traken by the Master in 1981. (TV: Logopolis)
- The Doctor states that he is not entirely sure of Turlough's species. (TV: Planet of Fire)
- The Doctor refers to the fact that he previously saw the Gateway during his fourth incarnation. (TV: Warriors' Gate)
- During her farewell to the Doctor, Nyssa says "I'm needed; you know that, Doctor." At an earlier point in her personal timeline but a later point in his, she told him that the same was true of him. (AUDIO: Winter, TV: The Caves of Androzani)
- Nyssa refers to their visit to London during the outbreak of the Bubonic plague in September 1666. (TV: The Visitation)
- The stars in E-Space go out as the universe dies. The same thing once happened to N-Space in an alternative timeline in which the Daleks were able to detonate the Reality Bomb. (TV: Turn Left)
- Tegan refers to her encounter with Alzarian spiders on Alzarius. (AUDIO: Mistfall)
- Nyssa recalls the death of the Monitor on Logopolis. (TV: Logopolis)
- Tegan once again says, "Rabbits!" (TV: Logopolis, Frontios; AUDIO: Psychodrome, The Emerald Tiger)
- Turlough recalls their reunion with Nyssa on Helheim in 3530. (AUDIO: Cobwebs)
- Nyssa's contact with the Sandmen reverses the rejuvenation that she experienced in India on 31 December 1926. (AUDIO: The Emerald Tiger)
- Nyssa refers to the Groves on Traken. (TV: The Keeper of Traken)
- The Doctor says he keeps a crank handle for when the TARDIS loses power. (TV: Death to the Daleks)
- Turlough jokes that it's been a while since someone has called him "boy" after being referred to as such by Captain Branarack. The Black Guardian used to refer to Turlough by this monicker. (TV: Mawdryn Undead et al.)
- The Sandmen whsiper "Ashes to ashes, dust to dust", a line used often by other charcters. The Seventh Doctor, for example, muttered this after taunting the Renegade Supreme Dalek into destroy itself. (TV: Remembrance of the Daleks)