Private detective Ferdinand Zankl is suspected of murdering his ex-girlfriend, the shelter manager Nunzia Rossi. He is arrested by the Passau police. At this point, of all times, Zankl is under great pressure to act because of another matter. The media had reported that excavation work was taking place in the Bavarian Forest to find relics from Roman times. Since Zankl buried the body of an Arab contract killer there last winter to protect Frederike Bader, he urgently needs to prevent the excavation team from coming across the body he has buried. However, his hands are tied due to his arrest. He calls Frederike for help. As an ex-police officer, she should secretly investigate and prove his innocence. Although Frederike never wants to have anything to do with Zankl again after what happened a few months ago, she accepts this deal to protect her daughter. Because Zankl is putting Frederike under pressure that he has information about her safety in witness protection. He only wants to give this to her if she helps him. She starts the investigation. She secretly finds out that the Czech puppy smuggler Jaroslav Kaiser was at the scene at the time of the crime. Jaroslav Kaiser is then arrested with the support of the Czech police. In a comparison with Zankl, Kaiser says that he also saw the private detective at the crime scene at the time of the crime. Since Zankl still has a clear relationship motive for the murder of Nunzia Rossi, he remains in custody. The Chief Inspector Grill and her colleague Piontek are delighted, because in secret, Grill would like to convict Zankl in order to score points in her new position. Frederike's first investigations thus prove to be a huge blow. Meanwhile, the archaeologists from the Bavarian State Office for Monument Preservation are approaching the place where Ferdinand Zankl buried the hit man Ahmed Bahdari - side by side with the remains of a Roman legionnaire. At the same time, Frederike comes across a second, promising lead in the murder of Nunzia Rossi on the farm of the popular Passau pop singer Ilka Unseld. The countdown is on, because the discovery of the double-occupied grave is only a matter of hours .

Die Donau ist tief. Ein Krimi aus Passau

In a supermarket in Passau there is an encounter that gives Frederike Bader's life another decisive turn: the ex-police officer rescues the private detective Ferdinand Zankl from a violent argument with a shoplifter. Frederike, until recently the group leader in the Mobile Task Force (MEK), it is easy to put the thief out of action. She no longer waits for the police to arrive. Her professionalism and her quick disappearance arouse Zankl's interest in his mysterious savior. He tracks her down and all alarm bells go off at Frederike: Is the private sniffer as harmless as he pretends to be? Or is it a threat? The suspicion does not seem unfounded. Ferdinand Zankl is not picky about his clients and assignments. At the moment, on behalf of a wealthy law student, he is observing a waitress whose boyfriend recently committed suicide. Which for Frederike, who misses her police work, raises the question: How could an 18-year-old Zankl's client be dangerous? While the ex-policewoman is drawn more and more into this enigmatic process, Ahmed Bahdari, a relative of the imprisoned clan chief, traces the whereabouts of Frederike and Mia in Berlin. His mission: the liquidation of mother and daughter .