Berlin, 1929. Detective Inspector Rath, was a successful career officer in the Cologne Homicide Division before a shooting incident in which he inadvertently killed a man. He has been transferred to the Vice Squad in Berlin, a job he detests, even though he finds a new friend in his boss, Chief Inspector Wolter. There is seething unrest in the city and the Commissioner of Police has ordered the Vice Squad to ruthlessly enforce the ban on May Day demonstrations. The result is catastrophic with many dead and injured, and a state of emergency is declared in the Communist strongholds of the city. When a car is hauled out of Berlin's Landwehr Canal with a mutilated corpse inside the Commissioner decides to use this mystery to divert the attention of press and public from the casualties of the demonstrations. The biggest problem is that the corpse cannot be identified.