The two detectives are dealing with a dramatic crime in Rostock. Two people die in the street. A young man stabs a woman to death and then executes himself. At the crime scene, König and Böwe are faced with a mystery, as there is no recognisable connection between Leon Schilling (Karl Seibt) and the manager Mona Färber (Nora Moltzen). The only clue is a message on Schilling's mobile phone - "Do it!" - the night before the crime. The message comes from Felix Lange (Sebastian Jakob Doppelbauer), a 28-year-old teacher, but he denies any involvement in the crime and claims to have known nothing of Schilling's intentions. But this is not the first time he has testified in a similar context: Felix was also in contact with Lara Trensbach (Samara Fry), a 19-year-old woman who also committed suicide recently in Rostock.