The Invisible Enemy (TV story)

Synopsis
A rocket with three men are near complete 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 have changed and 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 and, despite the efforts of the 3-man crew, is drawn into a strange 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 proceed to kill the resident crew and reveal their slowly changing faces. When the station supervisor, Lowe, realises that the men he knew are now trying to take over the base, he sends out a distress call.

The Fourth Doctor and Leela, now back in the refurbished console room, intercept the distress signal and proceed towards Titan. They pass through the same anomaly as the ship and the Doctor is struck by the energy, collapsing on the floor. Despite Leela's warrior instincts telling her that there is danger and evil on the station, the Doctor insists on answering 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 to recover, learning about the shuttle crew's strange behaviour. The Doctor meets Safran and Meeker, who use the energy discharge to further infect him and order him to kill Leela, who is immune and therefore useless to them. When the Doctor finds her, Meeker insists that he not in danger from the nucleus that infests the Doctor's body. Leela manages to kill 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 manages to resist the voice in his head and collapses, the signs of his infection receding. Lowe and Safran confer and decide that, while Safran prepares the station for incubating the virus, Lowe should 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 and they in turn start infecting more staff members. Marius becomes much more interested in the Doctor's case when his robotic dog, K9, examines the Doctor and reveals his extraterrestrial origin and his infection 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 and, since Leela is an instinctive being, it cannot infect her.

Marius prepares to operate on the Doctor's brain, which forces the virus to 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 two 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 along the way. They begin looking 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 down. The barricade slows the infected staff until one of them manages to infect 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 the Nucleus down. The Doctor tries to reason with it and 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 and compares itself to the human pioneers swarming out into space. Now that it has access to the Doctor's TARDIS, it has the opportunity to spread the virus through both 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 become enlarged, the next generation of the virus will be able to attack humanity on a macroscopic level. Leela disguises herself as an infected nurse and frees the Doctor so that they can take refuge in the TARDIS with K9. Without the dimensional stabiliser they are unable to leave and have to watch as Lowe and his infected brethren help the nucleus onto a shuttle for Titan.

K9 is able to stun Marius, so that the Doctor has time to examine his own blood and discover that Leela's clone has left him with antibodies against the virus. He is able to replicate the antibodies and cures Marius, who is able to replicate the cure for his staff. The Doctor plans to eradicate the virus spawning on Titan with the cure, but Leela is adamant that they should 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 that the infected are developing a resistance to her blaster. K9's weaponry is more effective, but his energy levels are dropping quickly. He instead draws the infected away, while the Doctor sneaks up on the spawning tanks. Lowe confronts him and causes him to lose the antibodies, but K9 uses the last of his power to shoot Lowe, who is then 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 deliver K9 to Marius, they find that the antibodies have been a success. Marius surprises the Doctor by asking him to adopt K9, as the 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
 * Nucleus Voice - 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.

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

Myths
to be added

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.
 * Marius' operating room is clearly a TV studio (it has no roof).
 * 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.
 * Lowe's "frozen" makeup changes between when he emerges from the freezer and when Leela brings him a cup of coffee.
 * 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 DWA: The Crocodiles from the Mist
 * This story occurs before VD: Crimson Dawn

DVD releases

 * Region 2 16th June 2008
 * PAL -


 * Region 4 4th September 2008
 * PAL -


 * Region 1 2nd 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 is aware of the problem but have decided to go on with the release as planned. Though they are trying to fix the problem for later copies of the DVD box set.

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.