Nicolai Holzer desperately confesses he 'must have murdered' his unfaithful lover Regina Mitzerlich, who was strangled in his home, but he can't recall the details. The team suspects a third party, hence also questions especially his jealous wife Vera, and the victim's separated husband, businessman Ralf Mitzerlich, as well as her colleagues, while looking for the third key as there was no breaking, but a tranquilizer administered without trace.