The Doctor and Romana whilst stranded in E-Space,arrive on a planet and discover a village. It's inhabitants, kept in ignorance, knowledge and science are forbidden so is any form of technology.The villagers serve and fear, the three " lords",who have ruled over them for a thousand years from the dark tower . Some villagers have been "chosen" and taken to the tower,never to return or be seen again.What is the secret the lords are hiding, and what has happened to those missing villagers?.