Rolf H. (Milan Peschel), single father of an autistic son, doesn't know what to do anymore. Financially and privately pushed more and more into a corner, he goes to the Staupen family estate to ask for help for his son. From his genealogical studies he believes he knows that their ancestors and his ancestors met in the Middle Ages and that the Staupen family cheated his family at the time and based their prosperity on it, which has continued to this day.
Confronted with the accusations and the request, the old Staupen (Markus Boysen) humiliatesRolf H. until he kills him in passion. That same night, his son Balthasar Staupen (Matthias Schweighöfer) finds his father and comes up with a plan. Fritz Dellwo (Jörg Schüttauf) and Charlotte Sänger (Andrea Sawatzki) suspect the perpetrator to be in the closest family circle, but they all have an alibi for the night of the murder. The investigations are getting more and more deadlocked. The brother and sister of the murdered man are found dead in quick succession. Are the Frankfurt commissioners dealing with a serial killer, and if so, what is his motive?