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.

A missing child is at the center of Inspector Helen Dorn's investigations. Mia, the four-year-old daughter of the wealthy businessman Hans Thomsen, has disappeared under mysterious circumstances. The family members are under shock; a kidnapping seems likely. While Mia's mother Inga tries to keep the family together and prevent an escalation, her husband wants to find his daughter on his own. But why does he head so assuredly for Rotterdam? After a difficult start at police HQ with her new partner Gregor Georgi, Helen Dorn begins to discover some very surprising things about Gregor. He, meanwhile, sets out to understand Helen better by uncovering her past…

On her way home after a celebration in her small, rural hometown, a young woman – Karla Petersen – is murdered. Helen Dorn, whose father is still in a coma, takes on the case. In the countryside, she meets local officer Tom Petersen, Karla’s brother. In spite of Dorn’s warnings not to get mixed up in the case, he relentlessly searches for his sister’s killer, suspecting friends and acquaintances alike.

Surveillance on an illegal arms trafficking case has spun out of control. Three Polish men are dead, two of them policemen. Mattheisen discloses his conspiracy theory to Helen Dorn: he is convinced that the weapons delivery was intended for an underground right-wing radical group, infiltrated by a mole from the State Office of Criminal Investigations. But before Mattheisen has a chance to tell Helen who is behind it, he is shot and killed with Helen’s service weapon. And Helen is found at the scene of the crime by her colleagues, gun in hand and no memory of what happened.

Helen Dorn has never been able to forget the case of a boy who disappeared 14 years ago. She had been forced to release suspect Ron Faber at the time, and the missing child was never seen again. When Helen learns from an Intrapol report that Faber was picked up in Hamburg after an accident with the dead body of a Chinese boy in the back of his van, she immediately sets off for the city.