The Murder in the Gymnasium is the debut novel by Yugo Aosaki and the first installment in his celebrated Urazome Tenma series. This classic locked-room mystery unfolds at Kazegaoka High School during the rainy season when Tomoki Ashima, the head of the broadcasting club, is found dead in the old gymnasium after school hours.

Detective Inspector Sendo and his subordinate Hakamada Yusaku from the Kanagawa Prefectural Police Criminal Investigation Division are assigned to the case. They quickly determine that the old gymnasium effectively became a sealed chamber at the time of the murder, as all entrances were either locked or under constant observation.

Suspicion falls on Nao Sagawa, the captain of the girls' table tennis club, who had finished her classes early and was in the old gymnasium around the time of the murder. Determined to prove her innocence, Yuno Hakamada, a first-year member of the table tennis club, seeks help from Tenma Urazome, the school's eccentric genius known for his reclusive nature and brilliant mind.

The novel features a large cast of characters from various school clubs, including the drama club, student council, broadcasting club, and table tennis club, all of whom become entangled in the investigation. As Tenma Urazome begins to unravel the mystery, readers are treated to a classic "challenge to the reader" section before the final revelations—a hallmark of golden age detective fiction that Aosaki skillfully incorporates into his modern narrative.