This film is about a group of high school students and teachers who get locked in the school after the swimming instructor is murdered. In South Korea, the high school student and swimmer Jeong Tae-yeon (Yoon Seung-ah) is found dead in the pool, apparently a suicide. Two years later, teacher Park Eun-su (Hwang Jung-eum) joins the high school, where Tae-yeon's stepsister Lee Se-Hee (Park Ji-yeon) is haunted by nightmarish visions and is bullied by the student Eom Ji-yun (Choi Ah-jin). Eun-su finds it difficult to get respect in the classroom and is backed up by an older teacher, Cha (Kim Su-ro). Se-Hee and her classmates are selected for an elite "study camp" held at the school during the summer break where 30 students study for their university entrance exams. The school's swimming trainer is murdered in the showers, and the words "When an innocent mother is killed, what son would not avenge her death?" found scrawled on a blackboard. A voice warns the students that they'll all be killed unless they can answer who is the murderer and why. The students and teachers find they're locked in the school when more deaths begin to happen.
Where are the students and teachers locked in at?
School