The Invisible Enemy (TV story)

Synopsis
A rocket with three men are near complete 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 Doctor himself. To save himself and others, the Doctor must undertake a dangerous journey.

Plot
The TARDIS is infiltrated by the Swarm - a space-borne intelligence that wishes to spread itself across the universe - and the Doctor is infected by its nucleus. The ship then materialises on Titan, one of the moons of Saturn, where the human occupants of a refuelling station have also been taken over.

The Doctor eventually collapses as a result of his infection, but first manages to relay to Leela the coordinates of a local hospital asteroid. At the Bi-Al Foundation, based on the asteroid, Professor Marius clones the two time travellers, miniaturises the clones using the relative dimensional stabiliser from the TARDIS and then injects them into the Doctor's body in the hope that they can find and destroy the nucleus.

The plan backfires as the nucleus escapes from the Doctor in place of the clones and is enlarged to human size. The creature arranges for itself to be taken back to Titan, where breeding tanks have been prepared for it.

The Doctor, now cured of its influence, enlists the help of K9, Professor Marius's dog-shaped robot computer, and sets a booby-trap that results in the breeding tanks being blown up, killing the nucleus. Marius gives K9 to the Doctor as a parting gift.

Cast

 * The Doctor - Tom Baker
 * Leela - Louise Jameson
 * Voice of K-9 - 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
 * Hedge - 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

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 K-9.
 * This story also re-introduces the 'old' white console room rather than the 'wooden' secondary console room which debuted in The Masque of Mandragora.

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
to be added

Discontinuity, Plot Holes, Errors

 * The clones of the Doctor and Leela should have been naked.

Continuity
to be added

DVD, Video and Other Releases
DVD release
 * This story has been confirmed for DVD release on 16 June, 2008 in a K-9 Tales Box Set. It will be released in the Box Set alongside K-9 and Company.

Target Novelisations

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