Though aiming for Hyde Park, the Tardis takes the Doctor where he's needed. He befriends a 'primitive' named by Leela, an outcast from the Sevateem tribe for speaking against Xoanon, their god. Leela meets the Doctor and believes he's the Evil One. The Doctor proves he isn't evil when he defends her against an attack.
Back in the tribe, Neeva is a prophet of Xoanon and speak to him, receiving instructions. Xoanon sounds suspiciously like the Doctor. When the Doctor sneaks in he notices Neeva speaks to Xoanon through a communicator and various other technical parts lay around, though not understood. The Doctor and Leela are soon captures, but it isn't long before they are able to escape.
Looking for the source of the transmission, and clues as to why Xoanon sounds like the Doctor, Leela brings him to the barrier where a large rock cliff is carved in his image. Leela says it's the face of the Evil One. Climbing up and into the images mouth, the Doctor is able to pass beyond a projected wall and into a crashed spaceship. It finally dawn on him, years before he was on the same planet and repaired the ships computer. But in Leelas time it was hundreds of years earlier.
Things suddenly become clear to the Doctor when he meets the sworn enemy of the Sevateem, the Tesh. When the Doctor repaired the computer years earlier he used his brain as a template for the circuitry and the computer now has a split personality. It's self aware self, and bits of the Doctor, because he forgot to wipe out his personality when he finished his repair of the computer. The computer is insane and tries to kill the Doctor.
Now with the help of the Sevateem, the Doctor is able to avoid the Tesh and repair the computer for good. In the process, he passes out for two days, meanwhile the two factions have declared a truce. The Doctor explains they are the descendants of the spacecraft. The Tesh, descendants of the Technicians and the Sevateem, descendants of the Survey Team. Now deciding to work together, the two factions decide to join forces. When they start fighting over who will be the leader, the Doctor quietly exits. When Leela is named, she also makes a hasty departure, chasing after the Doctor.
PLANET OF ORIGIN: Unnamed and far in Earth's future.
REASON FOR JOINING: Having been an outcast, Leela decides to follow the Doctor to the Tardis and begs him to take her with him. When he refuses, she runs into the Tardis anyway.
NEXT: A Timelords Best Friend