25 January 1975
Gladys Spencer, Peter Tuddenham (Voices) , Wendy Williams (Vira) [2-4], Kenton Moore (Noah) [2-4], Christopher Master (Libri) , Richardson Morgan (Rogin) [3-4], John Gregg (Lycett) , Gladys Spencer (High Minister’s Voice) , Stuart Fell [3-4], Nick Hobbs  (Wirrn Operators).
|Written by||Robert Holmes|
|Directed by||Rodney Bennett|
|Produced by||Philip Hinchcliffe|
In this four part adventure, The Doctor, Harry and Sarah accidentally arrive on an artificial satellite where the survivors of Earth lie in cryogenic suspension waiting to begin a new life. But The Doctor soon discovers that there has been a sinister intrusion… A gigantic insect has infiltrated the human ark. It is dead, but it was Queen of the Wirrn, sworn enemies of the Earth — and her egg sac was full. Something is terribly wrong and when the crew begin to awaken it soon becomes clear that some of them are not entirely what they seem…
The Doctor must find out how to destroy the Wirrn larvae before they absorb the last of the human race and become an invincible swarm. But this involves a desperate gamble with his own life — a gamble he must take if he is to save mankind.
- In Part One, the Title Sequence was tinted Pink and Green, making it appear brown rather than the usual blue (even the light on top of the TARDIS is full brown), this experiment was never repeated on any other stories.
- The Nerva Beacon sets are reused for Revenge of the Cybermen.
- The whole story bears resemblance to the Ridley Scott film ‘Alien’ released in 1979.
It is only mentioned once by Vira but Noah’s name is Lazer, Noah being a joke on his role on Nerva.
- No one but the regular cast take part in Part One of this story; the last time this occurred was episode one of The Edge of Destruction.
- Vira was written to be black and possibly Haitian, but this was changed by the director.
- The original script was written by John Lucarotti and he did get paid for his work; however script editor Robert Holmes had to do extensive revision and was the credited writer. Lucarotti’s story line included an ark, an uninhabitable Earth, humans who had ‘over-slept’ and aliens who had entered the ark in the meantime. Noticeable differences include the race of the aliens and that The Doctor went to the ark intentioanally and with purpose. Lucarotti’s aliens, named the Delk, had the ability to replicate instantly. This would have been Lucarotti’s fourth contribution to the show and his first since the William Hartnell era.
- Reissued as a two disk special edition