After four years in prison for the manslaughter of her father, Sara Manzer wants to look ahead. She has support for her new life - primarily from her friend Marlene, who takes her into her apartment. Sara, who has turned from a party girl into a reserved woman as a result of her imprisonment, wants to shake off memories and reorient herself. But then the police show up at her door. A former colleague was stabbed and old files of her case were found on him. She reluctantly admits that she spoke to Benno Rose before his death. He had new insights into her old case that should relieve her. Sara insists she had nothing to do with Rose's death. Which doesn't stop the inspectors from investigating.

What begins as a completely "normal" murder investigation takes on ever wider ramifications: The shopaholic Magnus Rosponi is found beaten to death in his apartment.

But neither his cheerful bowling friends nor Silke Haller, who recognizes the dead man as a teenage crush, can explain why the popular man had to die. Instead, Professor Boerne finds a strange, small object in the corpse. Thiel discovers parallel amorous entanglements. And when the Federal Office for the Protection of the Constitution turns up in the shady characters Muster and Mann, things get absurd.

Apparently Thiel and Boerne have stirred up a hornet's nest and even attracted the attention of an assassin. But how is it all connected? And what's the story with the little dog that loves eating bananas?