Trapped underground with the Cyber Controller and his acolytes, including the vermin-like Cybermats, the Doctor and company learn that they are to be turned into a new generation of Cybermen. To make matters worse, there is treachery and double-crossing amongst the humans.
Can the Cyber menace be made dormant before it spreads out to the galaxy once again, and will the Doctor, Jamie, and Victoria escape with their lives?
Frazer Hines, who played Jamie in these four BBC TV episodes from 1967, provides linking narration for the story. In a bonus interview, he also recalls the making of The Tomb of the Cybermen.