The wife of the well-known writer Roger Copenen is murdered. At first, everyone believes the woman became a victim of her husband’s deranged admirer. But the following string of ritual murders that shocked Helsinki leads detective Jessica Niemi to suspect that a serial killer is at work in the city. A mad fanatic who imagines himself an inquisitor stages horrific murders based on Roger’s bestseller, "The Witch Hunter." Is it possible to predict the next move of a criminal who knows every detail of the book better than even the author? Yet the further the investigation goes, the more obvious it becomes: the killer is not acting alone—adepts of a strange cult are involved, always one step ahead of the police. Jessica is sure that the fanatics won’t stop until they get what they want.