4th Period Mystery (2009)

4th period murder mystery. During fourth period, high schooler Da-Jeong finds her classmate Tae-Gyu dead in a classroom and Jeong-Hun standing in front of him with blood on his clothes. In order to stop Jeong-Hun from becoming the prime suspect, Da-Jeong must help him find the real murderer, who is still inside the school building, under 40 minutes before period four ends.