The Keeper of Traken

TV Season 18, Serial 6

Aired: 31 January 1981 - 21 February 1981

A Fourth Doctor story, the first appearance of Tremas, and by extension, the Tremas Master. For the first time, the Master regenerates through body-stealing. And because he's amazingly cruel, he steals the body of Nyssa's father. That really should have come up more often than it did.