Nocturnal distress signals, an empty yacht bobbing at dawn, and finally a missing Swiss shipyard owner: Klara Blum's latest case begins with a riddle on a wintry lake and requires cross-border cooperation with the Swiss colleagues. When Klara Blum discovers an aimlessly drifting, unmanned yacht practically in front of her front door on wintry Lake Constance, she finds possible traces of blood there. The Swiss shipyard owner Stähli, where the yacht was just overhauled, cannot be found. Klara requests administrative assistance from the Swiss police. Reto Flückiger from the Thurgau Maritime Police and his boisterous young colleague Marcel Steiner, who are supposed to be working with Klara and Kai Perlmann, suspect the shipyard owner Stähli, who has disappeared without a trace, of having smuggled drugs on a large scale.
Steiner, in particular, is convinced that Stähli has gone abroad. But then Stähli's body is found in the lake. Klara Blum and her Swiss colleagues are now investigating a murder together. However, despite all her sympathy for the charming Reto Flückiger, Klara has the impression that the two Swiss investigator colleagues are hiding something from her. Especially when Stähli's colleague Weingarten revealed to her that Steiner was not telling the truth on a crucial point. When Klara realizes that Reto is covering up for his young colleague's arbitrary actions, she becomes suspicious. She expresses her suspicion that the young, ambitious Steiner has something to do with Stähli's murder. And thus triggers a knee-jerk reaction in Steiner. He flees, head over heels.
Klara Blum's first 'Tatort' case with the Swiss Maritime Police colleagues was created as a co-production between SWR and Swiss television.