For every wrong answer, one student dies. As the countdown for college entrance exams begin, Chang Ahn High School organizes a special exam cram class for the top 20 students including girl-next-door Lee Na and classroom big shot Hyun Kang. Taught by Hwang Chang Wook and three other teachers, the class is festering with high-strung overachieving teens, some of whom are struggling with serious mental illnesses. In the middle of class, the television suddenly turns on. The students are shocked to see their classmate Hye Young drowning in a water tank onscreen. A voice asks them a sample exam question. Answer correctly, and the classmate lives. Answer incorrectly and...