A boy, the head of the broadcasting club, was stabbed to death by someone in the old gymnasium of Kazugaoka High School. It was right after school, raining heavily, and the scene was a locked room!　The police assume that the crime was committed by the head of the women's table tennis club, who was the only person in the gymnasium after classes ended early. Yuzuno, a member of the ping-pong club who was at the scene when the body was found, asks Tenma Urasome, who is known as the best genius in the school, to find out the truth for the suspected club leader.