Still mystified by his son's death, the father (Jo Sung-ha) of high school student Ki-tae (Lee Je-hoon) tries to track down his two best friends, classmates Hee-joon (Park Jung-min (actor)) and Dong-yoon (Seo Jun-young), to try to find an explanation. Through Ki-tae's classmate Jae-ho, the father meets Hee-joon, who says he cannot help as he moved schools "weeks before what happened to Ki-tae." Afterwards, Hee-joon berates Jae-ho for giving his phone number to Ki-tae's father but Jae-ho tells him that Ki-tae "went crazy" after he moved away. Hee-joon manages to trace Dong-yoon and urges him to contact Ki-tae's father and provide some answers. In parallel, flashbacks to the time gradually reveal what really happened, starting with Ki-tae's needling and bullying of Hee-joon and the latter's response.