It's the perfect evening: As Julien Bakker speeds across Lake Constance in a motorboat with his beautiful companion after a visit to the lakeside terraces, they're both tipsy and have eyes only for each other. They hear the desperate cries of a rubber boat driver too late. Because he doesn't want his affair with his companion, Flora Fitz, to be exposed—and because he's also under the influence of alcohol—Bakker flees the scene of the crime. There's no trace of the rubber boat's driver. He keeps the accident a secret from his wife, Annika. Instead, he finds a blackmail letter on his car the next morning…

A gorgeous morning on Lake Constance. Lea von Brahms sets out on her daily 2,000-meter swim. But she never makes it back to shore. Despite her desperate struggle, something drags her down into the depths. At first, Nele and Paul suspect Lea's boyfriend, the attractive personal trainer Malte Hummert.

Of all places, Mechthild is arrested right in front of the house of Thomas Steeler, the real estate tycoon who has just been murdered. She had been demonstrating there with others against speculators who are buying up apartments and houses around the lake and reselling them at a huge profit. For Nele, this is embarrassing and a real challenge. After all, Steeler had nothing but enemies.