After the events of Full Circle, the Doctor, Romana, K-9, and their newest companion/stowaway, Adric, arrive on a planet with a feudal society. The villagers live under the thrall of three lords—Zargo, Camilla, and Aukon—who dwell in a shadowy Tower, and experience a yearly ritual called “the Selection,” in which a sample of young villagers are taken to the tower, never to be seen again.