Young Tom, the seventh son of a seventh son, starts work as an apprentice for the village spook, whose job is to protect ordinary folk from "ghouls, boggarts, and all manner of wicked beasties.

Tom is dismayed when his master the Spook decrees that they will be spending the winter on gloomy and forbidding Anglezarke Moor but soon discovers the reason for his master's decision, as they tangle with two dangerous witches and struggle to keep a dark mage from resurrecting an ancient evil.

As sixty-year-old John Gregory reflects on the past, he reveals how the world of ghosts, ghasts, witches, and boggarts was exposed to him and he later became the Spook, even though his first intention had been to join the priesthood.