4th Period Mystery (Eng sub)

Jeong-hun is the best student in her school ... smart, popular and a successful future. His rival Tae-gyu, takes every opportunity to tease him verbally and physically, and the two enemies are known among the other students. One afternoon, Tae-gyu fight with Jeong-hun who makes a threat with a knife ... an act that is witnessed by another student. Jeong-hun departs from the situation but soon after the start of the 4th period returns and finds he killed Tae-gyu. The boy was stabbed several times and still in shock, Jeong-hun picks up the bloody knife on a nearby table, just in time to another colleague enters the room. Her name is Da-jeong, a lonely and obsessed with murderers and why it is known as "witch curtain" or "curtain head" because of her hair which is fallen down on his face (inspired by j-horror). Da-jeong is a quick survey of the situation before deciding that Jeong-hun is innocent of the crime, but they have less than an hour to find the real killer before the end of 4th period class when the body will be discovered. The couple set out to find the killer, and soon discover that almost everyone is a suspect ... and even more disturbing, the killer is now behind them too.