Another adventure for Gallifrey's favourite son. The Doctor (Tom Baker) is captured by the tribe of the Sevateem after landing on a strange alien world. He is befriended by Leela (Louise Jameson), a savage young warrior who tells him that her people recognise and fear him as the Evil One. Intrigued, the Doctor discovers that his own face is carved on a local rock face, reputed to be the home of the god Xoanon. Is the Doctor in some way responsible for Xoanon's presence, and can he prevent tribal warfare from breaking out? Also included is Louise Jameson's appearance on 'Swap Shop' to publicise her debut as Leela.