A group of winter travelers making their way through the mountains of medieval northwest England find themselves stalked by a mysterious and brutal force. Led by the Irish healer Molly and told from the viewpoint of Hob, a young apprentice, the small troupe must protect against the unseen threat as it pursues them first to a monastery, then an inn, and ultimately a Norman castle called Blanchefontaine. At each place, the creature strikes, leaving death in its wake. The castle, rather than granting safety, proves a trap for the creature is within the walls and hungry for more blood. Hob must rely on his wits and his adopted family to survive, slowly coming to realize there is more to them than he thought as secrets and mysteries are revealed.