As the Spook's apprentice Tom's first duty is to protect the County from the dark. But now Mam needs his help in her homeland of Greece. One of the most dangerous of the old gods, the Ordeen, is about to return there, bringing slaughter and devastation. Meanwhile, the Devil himself is still loose and if he and the Ordeen join forces, a new age of darkness will descend.

Mam has summoned a powerful group to her side but among them are Tom's old enemy, the Pendle witches, including the assassin Grimalkin, and the cunning clan leader Mab Moldheel. Can Tom go against all the Spook has taught him and ally himself to the witches? What is the secret that Mam is keeping from him? And what sacrifices must be made in the battle against the dark?