In order to return the evidence to the local police station, Satoshi Itomura and Shigeru Muraki of the Science Research Institute came to Miyazu Bay together. There they met Ishigami Kazushi, a detective from the Miyazu Central Police Station, who was chasing the suspect, and helped him catch the suspect. After that, Muraki was seasick, so Itomura and Muraki went to a nearby small hotel to rest. At this time, they received a call from the Special Countermeasures Office that the former Minister of Economy, Trade and Industry of Kyoto City, Nobuhiko Otowa, was found shot dead at home, and the suspect in this case was Toshiki Mizushima, the owner of the hotel where Itomura and his friends were. Mizushima took advantage of Itomura's temporary departure from the hotel and escaped. Afterwards, Itomura found a strange key on the shrine in the store. According to Muraki's identification, it was an antique key that had been made for 50 years. On the other hand, the police found that the gun used in this shooting case was the gun used when the son of the former Minister of Otowa, Takashi, was shot dead 5 years ago. At that time, Takashi and his father were working hard to introduce wind power generation projects. After he was shot, the police first suspected the environmental groups that opposed him, but the case came to a standstill due to insufficient evidence. Are the two cases related? At this time, Mizushima's girlfriend Maiko Ogawa and the daughter of former Minister Otowa, Miyazu City Councillor Ritsuko, and others surfaced one by one. At the same time, the gun that was used twice sounded again. What happened this time?