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.