The 75th anniversary of the founding of a choir is celebrated in a hotel. At the party we sing, drink and dance. August Bark is also particularly cheerful and, during the evening, gives life to a provocative dance with the young and charming Irene Eppler. Shortly thereafter, the girl is found killed in her hotel room: she had a basal skull fracture. Chief Inspector Derrick begins to investigate trying to reconstruct the facts based on the testimony of those present. While it's not easy to identify the killer, Derrick has an idea as to who might be the culprit.

After an afternoon spent in Munich, Ellen Theiss, a young student from a provincial college, does not return to the institute. Her lifeless body is found along the path through the woods that leads from the train station to the college. The news of his death caused panic among the companions: six months earlier, in fact, another girl had been murdered in similar circumstances. During the investigation, Derrick realizes that Ellen's death is to be connected to the crime that took place some time before and he devises a plan to frame the killer.

The lifeless body of the owner, Martha Balke, is found in a country house. For Derrick the case seems simple enough: the victim's husband, Alfred, inherits a great fortune with Martha's death and the man now also has the possibility of living with Roswitha, his young lover. Meanwhile, Marta's twin sister Johanna returns to Munich from the United States. When Derrick meets her he has an idea that could be helpful in framing the killer.