Alarm in Düsseldorf: the body of a nurse has been found on the banks of the Rhine, and evidence at the crime scene recalls a series of murders that had terrified the area four years previously. Three women had been killed in exactly the same manner. The obvious connections to the old cases prompt the head inspector to appoint Helen Dorn as chief investigator. In order to solve the nurse's murder, the old cases must be reviewed, whereby Helen and her partner Georgi come upon suspects from among their own police colleagues.