The wealthy Hamburg gallery owner Elaine Troost dies mysteriously on a stormy fall night and her body is subsequently found in the bathtub by her daughter Gabrielle. The autopsy of the body reveals that her death was caused by violence. A witness testifies shortly afterwards that she saw the art forger Jan Vleuten outside the gallery owner's house on the night of the murder. He is nicknamed "the blonde monkey" because of his strange fondness for primates and his light blonde hair..