On the planet Telos, an archeological expedition from Earth discovers the lost tombs of the Cybermen. Some members of the expedition decide to revive the Cybermen, in hopes of forming an alliance to take over the Earth. The 2nd Doctor, Jamie and Victoria help the rest of the group defeat the Cybermen, re-freezing them in their tombs. Trevor Sigma is present on Terra Alpha to conduct a census for Galactic Central. The 7th Doctor and Ace arrive and help topple the oppressive government.
Placement is conjecture.
En route, Bennett kills a man and is arrested. The ship crashes on the planet Dido, where Bennett kills all the other colonists but Vicki, and most of the native people. Bennet tells Vicki the Didonians were responsible for the deaths, and takes on the identity of Koquillion to keep her in line. On the planet Dido, the 1st Doctor, Barbara and Ian encounter two survivors of a spaceship crash, Vicki and Bennett, who are being terrorized by a figure called Koquillion. Bennett is revealed as Koquillion, and the murderer of the other crash survivors and most of the native population.