Futako Tamagawa City, a small town 15 minutes by train from the city center. There, "Futaba Koitaro" who runs a small detective bureau and "Shirakane Sisters" who are his assistants. A certain fall season, the mediocre ones ruled, and every day that was kind of happy because it was mediocre. Koitaro Futaba was kidnapped by the Sakuratsuki group. This is because Koitaro, who shared the important inco of the leader of the group, made the mistake that the inco was eaten by the cat. Around that time, Futaki bought dinner and Sara ran away from Mafia with the money she came to the office for help. Koitaro is forced to participate in a boxing betting match to take responsibility, but he betrays his expectations and knocks out his opponent. Sakuratsuki's angry boss tries to shoot Koitaro's gun...