One day, a teacher by the name of Izumi is found stabbed to death in her wedding dress in the pool on the rooftop of Seishun High School. A classmate confesses to being her killer to Class 3C’s president Hibino Meina and Goshima, the detective in charge of the case. However, Meina detects inconsistencies in the incomprehensible method and motive for murder and has to refute the person, only for another classmate to step forward to confess. Why would her classmates claim to be the criminal?