[1] Benny and the Doctor land on Earth in the late 30th century, in order to find out more information about a missing alien space ship.

The Doctor discovers that the person behind his arrest, and also responsible for supporting the Earth Empire, is none other than Tobias Vaughn, the former head of International Electromatics and collaborator with the Cybermen.

Just prior to his "death" (in The Invasion), Vaughn transferred his memories and consciousness into a robot body.

Since then, he has been manipulating Earth history in order to trap the Doctor and gain the secret to time travel.

Roz and Chris, now framed by corrupt Adjudicator officials, agree to travel with the Doctor rather than face trumped-up charges.