Se-jin was once a famous pro golfer. One day, Se-jin’s older co-worker died because his drunk driving. He loses his voice because of this car accident and goes to an island in order to take a rest. And this encounter starts to change Se-jin and people of this island.

Se-hee is haunted by her step sister Tae-yeon who used to be a promising swimmer but suddenly killed herself in a swimming pool 2 years ago. During the summer vacation, she joins the study camp at school for upcoming college entrance exam with other 30 elite students. On the first night, when Se-hee finds a riddling passage scribbled in the desk, she soon sees a dead girl’s body hung upside down. Then the TV monitors are on and the students watch another friend crushed by his bike in the corridor. Since then, the succession of cruel killings occurs whenever they fail to answer the given questions in time. Meanwhile, the hidden truth behind Tae-yeon’s suicide is slowly revealed and terrified students struggle to death to undo the puzzle before they become the next victim.