Students at an elite high school, preparing for mid-term exams, are held captive and forced into a series of sadistic games. The students find themselves plunged into a deadly test where they are picked off one by one and held in impenetrable traps where they must rely on the amazing intellects of their classmates to be released, every time a question is answered incorrectly, a classmate meets their torturous, grizzly death. When it emerges that the students are being picked off according to a pattern, pupil Kang Yi-na understands exactly how much time she has to stay alive and figure out the mysteries of who is imprisoning them and what is the ghostly presence that stalks the school and seems to bind them all together, before the Death Bell rings for her. Starring controversial, K-Pop sensation Nam Gyu-ri as Kang Ni-ya and Kim Beom ('Boys Before Flowers').