Se-hee is haunted by her step sister Tae-yeon who was a swimmer that is promising however killed herself in a pool 2 decades ago. She joins the study camp for upcoming college entrance assessment together with other 30 elite students in school. At the very first night, even when Se-hee finds a passage scribbled at the desk, she sees a girl's body wrapped ugly. Subsequently the television monitors are on and the students watch the other friend crushed by his bike in the corridor. Whenever they fail to answer the given questions in time, since that time, the succession of killings does occur. The hidden facts behind the suicide of Tae-yeon will be revealed and terrified students struggle to death to undo the puzzle before they end up being the next victim.