Jo Sang-geun

During fourth period, high schooler Da-jeong finds her classmate Tae-gyu dead in a classroom and Jeong-hun standing in front of him with blood on his clothes. In order to stop Jeong-hun from becoming the prime suspect, Da-jeong must help him find the real murderer, who is still inside the school building, under 40 minutes before period four ends.

Harin (19), a repeater, wanders because she cannot find what she wants to do. For her, who dreamed of traveling to a distant city, a theater ticket comes in instead of leave city. Curiosity and passion for acting begin to sprout in Harin's heart after seeing an actress performing on stage. Invited to the theater company's practice room, Harin becomes more and more immersed in acting. Harin begins to step on the path of an actor step by step with the desire to be applauded on stage, but obstacles that can never be overcome appear in front of her.