The Doctor has taken his companions to paradise, or at least the closest thing he can find. A sun enclosed by an artificial sphere where there is no want, poverty, or violence.

While Chris learns to surf, meets a girl and falls in love with a biplane, Roz suspects an alien plot and Bernice considers that a Dyson Sphere needs an archaeologist like a fish needs a five-speed gear box.

Then the peace is shattered by murder. As the suspects proliferate, Bernice realizes that even an artificial world has its buried secrets and Roz discovers what she's always suspected- that even paradise has its snake.