It's summer at Tegernsee, and it's raining cats and dogs. The Mangfall, the lake's outlet, turns red. Is it a sign or just a simple biological reaction? Quercher, a former police officer from the LKA, is nearly broke. A job is supposed to get him back on his feet. The relatives of a RAF victim have new leads on the perpetrator and want Quercher as their investigator because they no longer trust the state. Quercher dives into the past of West Germany, learns about the entanglements of close friends at the LKA and wealthy puppeteers from the lake. Suddenly, he finds himself in the midst of a diabolical campaign of revenge by various groups. It's about life, death, and old scores. And soon, the Mangfall will truly become a case of blood.