Nikolaus Kaminsky is a former police profiler who has been living in seclusion for 20 years, with no contact with the outside world. Only his neighbor's daughter Simone manages to coax him out of his shell from time to time. When he threatens the 12-year-old with a knife for no apparent reason one day, detectives Jäger, Kraft, and Hoffmann are called in. The police are actually busy with a kidnapping case, but when Kaminsky casually leads the investigators to the solution of the case, a long-forgotten case of child murders suddenly becomes relevant again. The last victim of the serial killer, who remains unknown to this day, was Kaminsky's daughter. When Kaminsky then warns the police about a new kidnapping case, the suspicion arises that the killer, believed to be dead, is back at work.