The body of 25-year-old paralegal Karin Berling (Stefanie von Poser) is recovered on the banks of the Danube in Regensburg. The parents are stunned, especially since their daughter Karin was about to marry the Turk Cengiz Özgür (Baki Davrak). The husband-to-be reacted to the news of his death with horror, but initial research made it clear that his relationship with Karin was about to end. One cause was the contentious relationship with his future parents-in-law, another, the close relationship between Karin and Klaus Webert. Klaus Webert (Tobias Oertel), who has no alibi for the time of the crime, comes under suspicion, but Cengiz's brother Mehmet (René Ifrah) is also among the suspects when it turns out that he is strongly committed to the fundamentalist movement.
Commissioner Lucas realizes that she can only solve the case if she also understands the religious and political ties behind itKnowing how to decipher events. Karin's superior, the well-known lawyer Tansu Nasiri (Idil Üner), gives her valuable background knowledge. In the middle of an interrogation, the unbelievable happens. The lawyer is shot in an ambush and only at the last minute does Inspector Lucas manage to save Nasiri's life. Now the assumption is obvious that a political motive is also possible in the case of Karin. The political explosiveness of the case reaches a new dimension when Attorney General Stahmer (Jan-Gregor Kremp) intervenes. The situation escalates when Cengiz's sister Leyla (Pegah Ferydoni), an important witness, suddenly disappears.
The worst must be feared, and the massive threats against the lawyer Nasiri don't stop, they even extend to Inspector Lucas. One thing is becoming increasingly clear to her: that the lawyer Nasiri seems to know more than she is letting on..

A butter boat on the Danube: the entertainer Rolf Gembel (Max Tidof) straightens his hairdo, puts the obligatory flower in his buttonhole and hopefully heads towards the stage in order to sell as many blankets as possible today. And then the unbelievable: like a still life, peacefully wedged together, ten people in the auditorium. Unconscious? Dead? A sign of life can only be found in Greta Wache (Renate Becker). The elderly lady, unable to be questioned, was brought to the clinic by Dr. Sion (Hannes Jaenicke) admitted. Inspector Ellen Lucas must assume a murderous robbery as all valuables, jewelry and credit cards have been stolen.
Toni Kehring, who was helping part of the group as a nurse and was observed fleeing the ship, is suspected of having committed a crime. Mysterious, tooStatements by his wife Anne (Jenny Schily), who runs a mobile nursing service and had contact with some of the victims. And Gembel also seems to know more than he cares to admit. Suddenly there is a new clue to the case: Ellen's landlord Max (Tilo Prückner), who is in the clinic of Dr. Sion to observe his heart, tells of an intimate encounter between Anne Kehring and Dr. sion When detective Lucas finds out that some of the victims at Dr. Sion was being treated and she gets in touch with his father (Hans-Peter Hallwachs), who vigorously propagates the right to a self-determined death, things start to move in the case.
The situation escalated when shortly afterwards the body of the nurse Toni Kehring was fished out of the depths of the Danube. When Greta Wache breaks her silence, light comes into the darkness of the case...