The Invisible Enemy (TV story)

The Invisible Enemy was the second story of Season 15 of Doctor Who. It introduced the robot dog K9 as a companion to the Fourth Doctor.

Synopsis
A three-man rocket crew are nearly done with their mission to Titan Base until a course change puts the rocket in the path of a strange cloud in space. By the time they have arrived, they serve a sentient virus which threatens the galaxy. When the TARDIS picks up an emergency message, it flies into the cloud, infecting the Fourth Doctor himself. To save himself and others, the Doctor must undertake a dangerous journey.

Episode one
A small spacecraft flies through an asteroid belt. Despite the efforts of the three-man crew, it is drawn into an anomaly. An energy discharge strikes the ship and infects the computer with a virus, which declares "contact has been made"...

By the time the ship reaches Titan Base, the three crewmen have been infected also. They kill the resident crew and reveal their slowly changing faces. When the station supervisor, Lowe, realises the men he knew are now trying to take over the base, he sends out a distress call.

The Fourth Doctor and Leela, back in the refurbished console room, intercept the distress signal and proceed towards Titan. They pass through the same anomaly. The Doctor is struck by the energy, collapsing on the floor. Despite Leela's warrior instincts telling her there is danger and evil on the station, the Doctor insists they answer the mayday. The shuttle crew are already aware of the TARDIS's imminent arrival and prepare for the coming of "the Nucleus". Lowe tries to stop them, killing Silvey, but Safran and Meeker chase him into the cryogenic section and lock him in.

The Doctor and Leela separate and explore the station. Leela finds a frozen Lowe and helps him recover, learning of the shuttle crew's strange behaviour. The Doctor meets Safran and Meeker, who use the energy discharge to further infect him. They order him to kill Leela, who is immune and therefore useless to them. When the Doctor finds her, Meeker insists that he is not in danger from the Nucleus that infests the Doctor's body. Leela kills Meeker, but not before he has infected Lowe. As Lowe leaves to follow Safran, the Doctor creeps up behind Leela and aims a weapon at her back.

Episode two
The Doctor resists the voice in his head and collapses, his infection receding. Lowe and Safran confer and decide that, while Safran prepares the station for incubating the virus, Lowe shall protect the Doctor at all costs. When the Doctor insists on finding medical help, Lowe suggests the Bi-Al Foundation in the nearby asteroid belt. The Doctor gives Leela the co-ordinates before he puts himself in a coma and she pilots the TARDIS there.

The Doctor is taken to Professor Marius, an expert in alien diseases, who at first dismisses the Doctor as a spacenik. Lowe fakes an eye injury and infects a doctor with the virus. They begin infecting more staff members. Marius becomes much more interested in the Doctor's case when his robotic dog, K9, reveals the Doctor's extraterrestrial origin and that he is infected by a virus residing in the mind-brain interface. The Doctor wakes himself and discusses the virus with Marius and K9, who was built by the professor to replace the dog he left on Earth. They decide that the virus thrives on intellectual activity. Since Leela is an instinctive being, it cannot infect her.

Marius prepares to operate on the Doctor's brain, which makes the virus cause a shuttle to crash into the asteroid as a distraction, while the infected staff launch an attack on the operating theatre. Leela and K9 hold off the infected crew while the Doctor forms a new plan, preparing short-lived clones of Leela and himself before lapsing back into his coma. The Doctor's clone uses the TARDIS's dimensional stabiliser to shrink the clones to microscopic size so Marius can inject them into the Doctor's body.

Episode three
The clones make their way into the Doctor's brain, dodging electrical impulses and the Doctor's immune system. They look for the mind-brain interface, where the Nucleus has hidden itself, and any neural damage that may show the way. As they proceed, they discuss the complexity of the brain and how it operates.

Lowe demands Marius surrender the Doctor, so Leela and K9 destroy the service shaft and barricade the corridor to slow the infected. The barricade helps until one of them infects K9 with the virus. K9 is ordered to kill Leela, but she dodges the blast and is merely stunned, while K9 shuts himself down to reboot. Lowe infects Marius and kills Dr. Parsons, but the nurse escapes and finds K9 and Leela in the corridor. Lowe has himself cloned and is miniaturised and injected into the Doctor to stop the other clones.

The cloned Doctor and Leela cross the mind-brain interface and track down the Nucleus. The Doctor tries to convince it to leave, but the Nucleus asserts its right to survive and procreate like any other life form, explaining that it has hung dormant in space for millennia. It compares itself to the human pioneers swarming out into space. Now that it has access to the Doctor's TARDIS, it can spread the virus through time and space. The cloned Lowe is stopped by Leela's duplicate and the Doctor's phagocytes but, just as the Doctor's clone tries to shoot the Nucleus, the time limit runs out and the clones vanish. The Nucleus escapes from the Doctor's body through a tear duct and is enlarged by Marius to human size.

Episode four
The Nucleus explains to the now virus-free Doctor that, having used the dimensional stabiliser to grow, the virus's next generation can attack humanity on a macroscopic level. Leela disguises herself as an infected nurse and frees the Doctor so they can take refuge in the TARDIS with K9. Without the dimensional stabiliser they cannot leave. They watch as Lowe and his infected brethren help the Nucleus onto a shuttle for Titan.

K9 stuns Marius so the Doctor has time to examine his own blood and discover that Leela's clone has left him with antibodies against the virus. He replicates the antibodies and cures Marius, who can replicate the cure for his staff. The Doctor plans to eradicate the virus spawning on Titan, but Leela insists they simply blow it up. When the cure is ready, the Doctor borrows K9 from the Professor and heads for Titan Base.

The Nucleus arrives at the base just in time for spawning and enters the incubation tanks prepared by Safran. When the TARDIS arrives, Leela discovers the infected are developing resistance to her blaster. K9's weaponry is more effective, but his energy levels are dropping quickly. He draws the infected away while the Doctor sneaks up on the spawning tanks. Lowe confronts him and makes him lose the antibodies, but K9 uses the last of his power to shoot Lowe, who is absorbed by the swarm. Leela kills Safran with her knife while the Doctor alters his plan and rigs the refuelling tanks to blow. They escape the base with K9 just in time to see the massive explosion, amplified by the methane in the atmosphere, from orbit.

Returning to the Bi-Al foundation to restore K9 to Marius, they find the antibodies have been a success. Marius surprises the Doctor by asking him to adopt K9; weight requirements will not allow the professor to take his robot dog with him when he returns to Earth. K9 happily accepts the situation and departs with the Doctor and Leela, leaving Marius to wonder if the robot is TARDIS trained.

Cast

 * The Fourth Doctor - Tom Baker
 * Leela - Louise Jameson
 * Voice of K9 - John Leeson
 * Lowe - Michael Sheard
 * Safran - Brian Grellis
 * Meeker - Edmund Pegge
 * Silvey - Jay Neill
 * Crewman - Anthony Rowlands
 * Nucleus - John Scott Martin
 * Voice of Nucleus - John Leeson
 * Professor Marius - Frederick Jaeger
 * Parsons - Roy Herrick
 * Cruikshank - Roderick Smith
 * Marius' Nurse - Elizabeth Norman
 * Reception Nurse - Nell Curran
 * Opthalmologist - Jim McManus
 * Hedges - Kenneth Waller
 * Medic - Pat Gorman

Crew

 * Assistant Floor Manager - Tony Garrick, Christabel Albery
 * Costumes - Raymond Hughes
 * Designer - Barry Newbery
 * Film Cameraman - Nick Allder
 * Film Editor - Glenn Hyde
 * Incidental Music - Dudley Simpson
 * Make-Up - Maureen Winslade
 * Producer - Graham Williams
 * Production Assistant - Norman Stewart
 * Production Unit Manager - John Nathan-Turner
 * Script Editor - Robert Holmes
 * Special Sounds - Dick Mills
 * Studio Lighting - Brian Clemett
 * Studio Sound - Michael McCarthy
 * Theme Arrangement - Delia Derbyshire
 * Title Music - Ron Grainer
 * Visual Effects - Tony Harding, Ian Scoones

Biology

 * K9 states the first successful cloning experiments were carried out in the year 3922. He adds that "the Kilbracken holograph cloning technique replicates from a single cell a short-lived copy. Efficiency of individualisation not completely guaranteed."
 * Professor Marius is said to be an expert in extraterrestrial pathological endomorphisms.

The Doctor

 * Leela tells the receptionist that the Doctor is from Gallifrey which she believes to be in Ireland.

Culture

 * Marius presumes that the Doctor is a spacenik.

TARDIS

 * The TARDIS' dimensional stabiliser just so happens to fit into Marius' equipment.
 * Leela seems to have learned how to operate the TARDIS since she is able to program it to go to the Bi-Al Foundation.

Theories and concepts

 * Leela's antibodies are a time paradox: she is descended from people who left Earth after this story, and by being present in 5000 AD she gives humanity the antibodies she has always possessed (as a result of her trip to 5000 AD!)

Story notes

 * This story had the working titles; The Invader Within, The Enemy Within and The Invisible Invader.
 * This story was listed on the 1970s sound effects LP as "The Enemy Within" which would go on to become the second-hand title given to the 1996 television movie.
 * This is the story which introduced K9.
 * This story also re-introduces the 'old' white console room (though slightly redesigned by Barry Newbery) rather than the 'wooden' secondary console room which debuted in The Masque of Mandragora.
 * Leela is left-handed, or at least writes with her left hand. Actress Louise Jameson is right-handed, but chose to make Leela a left-handed writer in order to increase her awkwardness at this task.
 * This is the only story in which the monitor on K9's left side actually displays anything.
 * John Leeson is credited as Nucleus Voice for Part One, while for Parts Two to Four he is billed as Nucleus & K9 Voice on-screen and as Nucleus Voice and K9 in Radio Times.
 * The introduction of K9 Mark I marks the beginning of an almost seven year span of stories featuring at least one non-human companion which would last until the departure of Turlough, a native of Trion, and the destruction of Kamelion, a shape-shifting android, in DW: Planet of Fire in 1984. The relevant non-human companions who appeared in the interim were K9 Mark II, the first and second incarnations of the Time Lady Romana, the Alzarian Adric and the Trakenite Nyssa. Turlough and Kamelion would be the final non-human companions to appear in a televised Doctor Who story until the Auton duplicate of Rory Williams was introduced in DW: The Pandorica Opens / The Big Bang in 2010.

Ratings

 * Part 1 - 8.6 million viewers
 * Part 2 - 7.3 million viewers
 * Part 3 - 7.5 million viewers
 * Part 4 - 8.3 million viewers

Filming locations

 * Ealing Television Film Studios, Ealing Green, Ealing
 * Bray Studios, Slough
 * BBC Television Centre (Studio 6), Shepherd's Bush, London

Production errors

 * When the TARDIS first arrives on Titan, in the background you can see one of the relief ship crew still helmeted.
 * The first shot of the Bi-Al Foundation shows it with the damage later caused by the shuttle crash.
 * When K9 blasts a chunk out of the wall, it's obviously a pre-cut segment.
 * The knife that Leela kills Meeker with is very obviously loosely sewn to his clothes. Notice how it wobbles back and forth after he falls.
 * In the very first scene, as the Doctor collapses to the ground, a person can be seen moving in the back of the set.
 * When K9 shoots one of the infected men, the blast beam appears to come out of his eyes, then moves down to his snout as the camera moves.
 * The countdown clock in Marius' lab speeds up and slows down as needed for the plot.
 * When the Doctor is congratulating himself on blowing up the Swarm, the shadow of a boom mike can be seen.

Continuity

 * K9 joins the Doctor and Leela. He departs with Leela in DW: The Invasion of Time.

Timeline

 * This story occurs after DWAN: The Crocodiles from the Mist
 * This story occurs before VD: Crimson Dawn

DVD releases

 * Region 2 16 June 2008
 * PAL -


 * Region 4 4 September 2008
 * PAL -


 * Region 1 2 September 2008
 * NTSC -


 * This story was on DVD release on 16 June 2008 in a K9 Tales Box Set. It was released in the box set alongside K9 and Company.
 * Early versions of the box set feature a fault on The Invisible Enemy disc. A scene from half way through episode 3 is skipped and appears after the closing credits. 2 entertain was aware of the problem but decided to go on with the release as planned. They are trying to fix the problem for later copies of the DVD box set.

Contents:
 * Commentary by Louise Jameson, John Leeson, Bob Baker and Matt Irvine
 * Dreams and Fantasy - Making-of documentary
 * Studio Sweepings - Raw studio footage from the serial
 * Visual Effect - Modelwork in The Invisible Enemy
 * Blue Peter - Clip from an episode featuring K9
 * CGI Effects - Option to watch serial with some original effects shots replaced by new computer-generated images
 * Trailers and Continuity
 * Photo Gallery
 * Production Subtitles
 * Radio Times Listings
 * Easter Egg - K9 appears on The Generation Game. To access this hidden feature, press left at Visual Effect on the Special Features menu.

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

K9 Tales
This story and K9 and Company were released as a DVD box set in 2008.

Novelisation and its audiobook

 * Main article: Doctor Who and the Invisible Enemy


 * Novelised as Doctor Who and the Invisible Enemy in 1979 by Terrance Dicks.