An airplane flying at an altitude of 10,000 meters was hijacked. A teenage boy, Kimihiko Kimizuka, was appointed as an assistant by a mysterious girl, Siesta, who called herself a detective, and went to the cockpit. There, a man codenamed "Bat" took the captain of the plane hostage. "Bat" demanded that Siesta deduced "why they hijacked the plane" as a condition for releasing the hostages.