A dead man in the subway calls the inspectors Ritter (Dominic Raacke) and Stark (Boris Aljinovic) into action. It is the building contractor Horst Baumann, who had already come to the fore in the past due to a spectacular company bankruptcy. After a long stay abroad, he returned to Berlin to renovate real estate with the help of his attractive wife Alissa (Muriel Baumeister) and his opaque partner Alsfeld (Hansjürgen Hürrig). The investigations quickly bring the inspectors on the trail of the craftsman Rothe (Bruno F. Apitz), who was ruined by bankruptcy at the time.
Did he want revenge on Baumann? While Stark learns that there was a crisis in the marriage between Alissa Baumann and the murder victim and that both of them had a violent onehad an argument, Ritter leads the search for the murderer back to the scene of the crime: in the underground catacombs of Berlin. During his research, he meets Daniel (Marlon Kittel), who, as a supervisor, undertakes illegal tours into the underground labyrinth with troubled young people. But not only he knows his way around here. In the network of corridors and shafts, Ritter meets the weird artist and hermit Gregor (Harald Schrott). Both Daniel and the artist seem to be hiding a dark secret here. The homeless woman (Anke Sevenich) could shed light on the investigation.
The murdered man watched this over and over again using a video recording. But who is she? And where is she? Knight and Stark are faced with a mystery - above and below ground..