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 creatures of the dark hunt for the witch assassin Grimalkin, who carries the captured Fiend's head, Spook's apprentice Tom tries to find a way to finish this terrifying evil once and for all.

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."

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.

Adventure is coming, and Barclay Thorne is ready to answer. Something is wrong at the Sea. The weeping tide, a carnivorous algae bloom, is eating up all the fish. Beasts are terrorizing the nearby Elsewheres. And Lochmordra, the Legendary Beast, is rising at random and swallowing ships whole. Barclay's teacher, the famous Guardian Keeper Runa Rasgar, has been summoned to investigate, and as her apprentice, Barclay gets to join too. But Runa's nemesis...