"He would learn nothing from the internal organs — and for a very good reason: there was nothing there. The dead girl's body was literally just skin and bone."

A New Age cult worships a hideous god — or is it a demon? — called the Skang. What possible connection can it have with the mysterious corpse on Hampstead Heath?

Sarah Jane Smith enlists the help of the Third Doctor and the Brigadier, and their investigations take them halfway across the world, to a remote island that has been turned into a paradise for the followers of the cult.

But the island is not what it seems, and neither is the Skang itself; and the Doctor and his companions are faced with the task of saving not only its devotees but the whole of mankind from a loathsome death.