Synopsis: A planet colonized by earth long ago is home to werewolves, wyverns, and intelligent unicorns. On top of everything else, it must suffer through the third invasion of the devils from the blood-red demon moon that returns every thousand years. Two young men and a young woman are the keys to finding the secret of the demon moon, and the terror it brings. An interesting mixture of fantasy and science fiction. Williamson's 50th novel.