The Invisible Enemy


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The Invisible Enemy

Serial Code


First Transmitted

1 October 1977

Final Ratings






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Regular Cast

Tom Baker (Doctor Who), Louise Jameson (Leela)

Guest Cast

John Leeson (K9), Michael Sheard (Lowe), Brian Grellis (Safran) [1-2, 4], Edmund Pegge (Meeker) [1], Jay Neill (Silvey) [1], Anthony Rowlands (Crewman) [1], John Leeson (Nucleus Voice)*, Frederick Jaeger (Professor Marius) [2-4], Roy Herrick (Parsons) [2-3], Elizabeth Norman (Marius’ Nurse) [2-3], Nell Curran (Receptedition Nurse) [2], Jim McManus (Opthalmologist) [2-4], Roderick Smith (Cruikshank) [2-3], Kenneth Waller (Hedges) [2], Pat Gorman (A Medic) [3-4]&dagger,, John Scott Martin (Nucleus) [3-4].


Written by Bob Baker And Dave Martin
Directed by Derrick Goodwin
Produced by Graham Williams


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 arrive, they have come under the control of a sentient virus which threatens the galaxy. When the TARDIS picks up an emergency message, it flies into the cloud, infecting The Doctor. To save himself and others, he must undertake a dangerous journey.


  • This is not the only occasion where a Doctor shall encounter a clone of himself, in Project: Lazarus, the Seventh Doctor encounters an organisation called the Forge, who have created countless clones of the Sixth Doctor due to a cellular degeneration problem with their technology, transferring the memories of the previous clone to the next one so they believe themselves to be the same Doctor throughout.
  • K9 marks the first of only a small number of mechanical companions, other examples of these include the Fifth Doctor’s companion Kamelion (The King’s Demons to Planet of Fire), the Seventh Doctor’s companions Cat and Antimony (Companion Piece andDeath Comes to Time, although both of these may take place in alternate universes), and the Eighth Doctor’s companion Compassion (Joined him in Interference: Book Two, mutated into a TARDIS in The Shadows of Avalon).
  • 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 TV 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 display
  • Order the DVD
  • trailer

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