Robbie Coltrane stars as Fitz, a brilliant but flawed, wise-cracking criminal psychologist who looks behind the evidence of a murder to discover what lies within the criminal mind. Schoolgirl Joanna Barnes, a member of a religious cult, is having an affair with the married leader of the group, Kenneth Trant. When confronted about it, he and the other leaders abduct her and the police reluctantly call in Fitz to help find her. Discovering that Joanna is pregnant by Trant, his wife and sister, trying to protect the reputation of both him and their church, ritually murder her. The final piece of this puzzle is supplied by one of Joanna's friends and in a final showdown in the group's church, things reach a destructive conclusion.