One will die for every incorrect answer.
In a prep-class for year-end exams, a sadistic killer puts the students through mind-games in order to save each other.
Lee Beom-soo
Hwang Chang-wook
Yoon Jung-hee
Choi So-yeong
Nam Gyu-ri
Kang Yi-na
Kim Bum
Kang Hyeon
Son Yeo-eun
Yoon Myung-hyo
Lee Eol
Security guard
Kim So-hee
Ji-won's mother
Kong Jeong-hwan
Lee Chi-yeong
Ham Eun-jung
Kim Ji-won
Yang Ji-won
Min Hye-yeong
Lee Chae-won
Yeom Ji-hyang
