The Invisible Enemy is the second serial of the 15th season of the
British science fiction television series Doctor Who, which was first
broadcast in four weekly parts on BBC1 from 1 to 22 October 1977. The
serial introduced the robot dog K9, voiced by John Leeson.In the
serial, an intelligent virus intends to spread across the universe
after finding a suitable spawning location on the moon Titan.Mankind
is colonising 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 it over 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 Fourth Doctor, but he is unaffected. 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 Invisible Enemy (Doctor Who) Biography, NetWorth, Height, Age, Weight, Family, Married, Son, Daughter