4th Period Mystery 2009

Jung-hoon, Yoo Seung-ho, is the top student at his school, respected for his quick thinking and calm approach under pressure. His rival, Tae-gyu, Sang-geun Jo, thrives on provocation and uses every chance to undermine him, and the two are known enemies among their peers. One afternoon, Tae-gyu pushes Jung-hoon too far and the latter brandishes a knife in a heated moment, an act witnessed by another student. Jung-hoon walks away, but as the 4th period begins he returns to a grimmer scene: Tae-gyu lies dead, stabbed repeatedly. In shock, Jung-hoon picks up the bloody knife from a nearby desk, just as Lee Da-jeong, Kang So-ra, arrives and catches him in a incriminating position.

Lee Da-jeong believes in Jung-hoon’s innocence and insists on helping him unravel what happened, recognizing that time is against them because in 40 minutes the rest of the class will return and the body will be discovered. The pair team up to search for clues and quickly realize that almost everyone in the room could be a suspect. The investigation unfolds with careful attention to motive and opportunity, while an unseen threat begins to close in on them as well, turning the high school into a tense maze where trust is scarce and danger lurks around every corner. As they dig deeper, the atmosphere grows more claustrophobic, and the stakes rise: catching the real killer becomes not only a matter of clearing Jung-hoon’s name but of staying one step ahead of a killer who has his sights set on them.