4th Period Mystery (4-kyo-si Choo-ri-yeong-yeok)
During fourth period, Da-Jeong finds her classmate, Tae-Gyu, dead in the classroom—with Jeong-Hun standing next to him, covered in blood. To save Jeong-Hun from accusations, Da-Jeong must help prove he is not the perpetrator. There are only 40 minutes left before the bell rings, and the real killer is still on the loose at school.