Arda Turan, former high-performance swimmer, has just started her service at the Duisburg Water Protection Police, where there is already the first corpse. Stefan Buhl is dead at the edge of the harbor. What Carsten Heinrich von der Kripo quickly identifies as a fatal occupational accident raises doubts among Gerhard Jäger, who was sentenced to the "WaPo" by the murder commission. A look at the corpse tells him it was murder. But leave the investigation to the Kripo? - No chance!

A driverless boat on the Rhine initially also alerts the Kripo, because there are traces of blood on deck. But the supposed blood turns out to be a red rust protection paint and so the case falls within the competence of the "WaPo". Jäger quickly realizes that something is wrong and sets out together with his colleagues Arda Turan and Frank van Dijk in search of the owner. However, Duisburg entrepreneur Niklas Brandt, who owns the boat, has disappeared and his wife's behavior is quite strange. The colleagues at WaPo want to take a closer look at this. An observation confirms her suspicion: The man was kidnapped.

The Kripo is on the verge of taking up a drug ring and delivery, while the "WaPo" is chasing a wild angler who has so far been able to escape its access every time. Arda and Frank are suddenly locked up when checking a refrigerated container! No wonder, because the drugs are hidden here. The two manage to send a message and its location, but the joy does not last long, because the container is loaded! The situation is threatening: How long can they survive in the cold? Hunter and secretary Lena go in search of her colleagues and desperately try to find the container.

A homeless person is found dead in the inner harbor. Carsten Heinrich von der Kripo quickly dismisses the case as suicide and leaves the "WaPo" to identify the victim. Marcel Bautz is already waiting impatiently at the guard: He misses his best friend - who turns out to be the dead homeless person. Bautz is sure that Hacki, whom he only knows by this name, was killed and the injuries of the dead also indicate this. But who would have a motive?

The jeweler André Fischer is robbed. The police immediately close all roads so as not to let the thieves escape. But there is a security vulnerability: the port. Thanks to Jäger's real smell, the colleagues of the WaPo go on a chase and can stop a suspicious ship. But not only the jewel robbers are on board, but also Frank van Dijk's father!

Pub owner Helga, who makes the colleagues of the "WaPo" behind the counter happy, is attacked and shot. The attack on the landlady of her regular pub is causing horror. The entire staff of the district wants to clarify the case as soon as possible and hunt down the perpetrator. Even hunters and arch-rival Carsten Heinrich von der Kripo form an alliance for this. All testimonies burden Tarik Alkan, who was the first to help Helga, but was the family father really the perpetrator?

What begins as a nice evening on the banks of the Rhine ends with an unexpected mission for Commissioner Arda Turan. The former high-performance swimmer pulls a lifeless diver out of the river. But was that really an accident? Jäger's suspicion is also aroused and the WaPo team begins the investigation. The dead man is Vincent Kraus, who ran a diving school on the Ruhr. His companion Sven Moeller quickly becomes the main suspect, as he has repeatedly concealed company money...