At the end of September, when the heat was unbearable, a "gunman" suddenly appeared on the Tokyo Provincial Line tram. On a moving train, the beautiful girl Kaori Ichinomiya was shot dead. She was shot in the upper heart and died on the spot. A small piece of cloth embroidered with a skull was left at the scene. The police intervened in the investigation, and many clues pointed to the Sasaki mansion, and relevant personnel such as Sasaki Mitsuyoshi, Akahoshi Ryuko and others were full of doubts. After that, Kaneko Futaki and Itoko Miura were shot to death on the Provincial Line Tram one after another, with the same method of committing the crime. While the police were struggling, Akahoshi Ryuko was also attacked and injured. Private detective Homura Roku appears to assist in the investigation. Can he solve the mystery behind this series of cases? Who is the real "shooter"?
