The Invisible Enemy (Doctor Who)

093 – The Invisible Enemy
Doctor Who serial
Literally lost in his own head, the Doctor and Leela search for the nucleus of the virus
Cast
Doctor Tom Baker (Fourth Doctor)
Companions Louise Jameson (Leela) John Leeson (Voice of K-9 Mk. I)
Others Michael Sheard — Lowe Brian Grellis — Safran Jay Neill — Silvey Edmund Pegge — Meeker Anthony Rowlands — Crewman Frederick Jaeger — Professor Marius John Leeson — Nucleus Voice Roy Herrick — Parsons Elizabeth Norman, Nell Curran — Nurses Jim McManus — Ophthalmologist Roderick Smith — Cruikshank Kenneth Waller — Hedges Pat Gorman — A Medic John Scott Martin — Nucleus
Production
Directed by	Derrick Goodwin
Written by	Bob Baker Dave Martin
Script editor	Robert Holmes
Produced by	Graham Williams
Executive producer(s)	None
Incidental music composer	Dudley Simpson
Production code	4T
Series	Season 15
Length	4 episodes, 25 minutes each
Originally broadcast	1–22 October 1977
Chronology
← Preceded by Followed by → Horror of Fang Rock Image of the Fendahl

Doctor Who and the Invisible Enemy

Author	Terrance Dicks
Cover artist	Roy Knipe
Series	Doctor Who book: Target novelisations
Release number	36
Publisher	Target Books
Publication date	29 March 1979
ISBN

The Invisible Enemy is the second serial of the 15th season in the British science fiction television series Doctor Who, which was first broadcast in four weekly parts from 1 October to 22 October 1977. The serial introduced the Doctor's newest companion, the robot dog K-9, voiced by John Leeson.

Mankind is colonizing space at a fantastic rate. Some human space travellers are cruising near the outer planets of the solar system with their ship on autopilot. The ship's computer, and soon the human crew, is possessed by a strange virus. Reaching their destination, Titan Base, they proceed to take over the base as a breeding ground. The station manager, Lowe is able to send out a distress call.

The TARDIS is travelling through the same region, and is infected by the virus. The infection passes to the Doctor, but he is unaffected for the moment. He and Leela hear the distress call and go to investigate. While there, the Doctor is overcome by repeated infections and is chosen, due to his incredible powers as a Time Lord, to be the host of the Nucleus of the Swarm. Leela is unable to be infected.

The Nucleus declares her a reject and orders that she be killed. The Doctor manages to break free of his infection and tells Leela how to get the TARDIS to the nearest medical centre. Accompanying them is Lowe, who has been infected, although the Doctor and Leela don't know this.

At the medical station, the Doctor's doctor, Professor Marius, introduces the group to K-9, a robotic dog he made to replace the real dog he had to leave on Earth. Professor Marius is baffled as to how to treat the Doctor's strange infection. Meanwhile, Lowe has been infecting the staff of the hospital.

Leela and the Doctor decide on a last-ditch strategy. They create clones of themselves, which can only survive for ten minutes due to problems with the technique. The clones will then be shrunk and inserted into the Doctor. There they will destroy the Nucleus and escape through a tear duct. In the meantime, Leela and K-9 fight off the infected staff of the hospital.

After a hazardous voyage through his mind, the Doctor's clone and Leela's clone are separated, and the Doctor's clone reaches the Nucleus. He has no weapons with which to destroy it, and it learns the intended escape route of the Doctor's clone, since the Doctor thought of it. Prof. Marius faithfully retrieves something from the tear duct and expands it to human size. It turns out to be the Nucleus. The Doctor is cured of his infection.