A group of students, including James, Mary, Jane, Ellis, and Eric, are at school when they discover that their teacher, Mr. Oms Back, has been fired. They decide to sneak into the school at night to cheat on an upcoming exam but soon find themselves being stalked and killed by the teacher, who is wearing a school mascot costume.
As the night progresses, the students try to escape but find the doors locked, and they are forced to navigate the school to survive. The teacher's motives become clear when it is revealed that he was having an affair with James, and he feels betrayed by James's actions.
The students try to find a way out, but the teacher continues to hunt them down. In the end, only one student, Mary, is able to escape by climbing a tree and then bludgeoning the teacher with a hammer. The next day, a friend who had stayed behind in the car sees Mary walking towards him, hammer in hand, and is relieved that he didn't join her friends the night before.
Here are the key facts extracted from the text:
1. The movie starts in a school where a teacher named Mr. Back is telling his students that only one student, James, got a good grade.
2. The students complain about not being able to retake the exam, and the teacher congratulates James on his perfect grade.
3. A girl named Mary asks James to convince the teacher to let them retake the exam.
4. The teacher, Mr. Back, is fired after an incident with James.
5. The students, including James, Jane, Ellis, and Eric, go to the school at night to find the exams they will have to take.
6. They discover that the sports teacher's office is a mess and find a diary belonging to the teacher.
7. The students decide to have a party in the school instead of studying.
8. Eric goes missing, and the others find him dead in the locker room.
9. The students realize they are trapped in the school and try to find a way out.
10. They discover that the school's mascot is the one who is hunting them down.
11. The students try to escape through the ventilation ducts but decide it's a bad idea.
12. They find a note that says "You should have taken notes" and realize it's a message from the killer.
13. The students try to barricade themselves in a room, but the killer finds them.
14. James reveals that he had an affair with Professor Oms Back, who is the killer.
15. The students try to escape, but the killer chases them down.
16. One of the students, Merit, is stabbed in the eye with a pencil.
17. The killer takes the keys to the front door, and the students try to escape.
18. Merit manages to escape and calls the emergency room, but the killer takes her phone.
19. Merit runs away and climbs a tree, where she attacks the killer with a hammer.
20. The movie ends with one of the students, who stayed in the car, seeing Merit coming towards them with the hammer.