Canapés, champagne, fireworks... and a dead body! Richard Kühn, managing director of a luxury toilet seat company, is murdered during a party - in a quiet little place of all places. The investigators are thrown headlong into the case on their night off...

Preparations for the "100 years of Lünen police station" anniversary celebration are in full swing, an event set to conclude with a tribute to outstanding investigative work. An honor the team surrounding Brandt and Wiesel might be worthy of considering their latest case: bar owner Robin Bürger has been found dead in his cooling chamber. The investigation proves to be increasingly complicated as everyone affiliated with it either tries to hide the truth or plot against one another. Soon, Brandt and Wiesel are certain that all of them are two-faced. How right they are with that assumption and how deeply the case will come to affect their own lives are the questions at the heart of this 5th "wieselflink and brandtgefährlich" film.