Parts: 2
Writer: David Whitaker
Airdates: 2 January 1965 - 9 January 1965
Production Code: L

Episode Titles: The Powerful Enemy; Desperate Measures

Doctor: first
Companions: Ian, Barbara, Vicki

Story: Inside a crashed spacecraft on the planet Dido, a girl named Vicki mistakes a blip on the proximity detector for a rescue ship. Her companion, the paralyzed Bennett, tells her not to get her hopes up and warns her against saying anything to Koquillion. The blip is, in fact, the TARDIS. The Doctor has been acting strangely since Susan's departure, and he elects to stay behind while Ian and Barbara explore.

Following their sighting of Vicki's spaceship, Ian and Barbara are approached by a menacing reptilian creature - Koquillion - who questions them angrily. When Ian goes to fetch the Doctor, Koquillion forces Barbara off a cliff and then traps Ian in the caves with a rockfall. The Doctor, who has visited Dido before, recognizes Ian's description of Koquillion as one of the native Didonians - a peace-loving race.

Why does Koquillion protect Vicki and Bennett yet terrify them, and why have the friendly Didonians apparently turned against their nature? To find the answers, the Doctor must uncover a vicious crime that could endanger all their lives.