The wife of famous writer Roger Koponen was killed. At first, everyone is sure that the woman has become a victim of a crazy admirer of her husband’s work. But a subsequent series of ritual murders that rock Helsinki leads detective Jessica Niemi to believe that a serial killer is at work in the city. A mad fanatic who imagines himself an inquisitor acts out the terrible murders from Roger's best-selling book "Witch Hunter". Is it possible to predict the next step of a criminal who knows every detail of the book better than the author himself? But the further the investigation progresses, the more obvious it becomes: the killer is not acting in alone, adherents of a strange cult are involved in the crimes, who are always one step ahead of the police. Jessica is sure that the fanatics will not stop until they get what they want.