Christer has shared most of his young life with his cousin Sophie. But when his aunt remarries and they move away to a large house in the country, he feels a loneliness he has never known before.
Then Sophie becomes ill, slipping in and out of consciousness. Clutching at straws, his aunt hopes that the sound of Christer’s voice might help to bring her round. He visits, as promised, and embarks on a quest for the mind of his cousin, lost somewhere in another dimension.
Following clues in her diary he plunges into a strange world of oppressed people, ruled by the Yendak, a cruel and violent race. If they find him, he will never get back home.