High school student Yu Seongbin, who has a nasty attitude and something rotten in his soul, has chosen the weak Han Gyuhwan as his victim. Since no one cares enough to stop the violence Gyuhwan endures, his mind festers with fantasies of standing up to his bully and the useless adults around him, picturing himself pulling out a shotgun to exterminate them all. When their class goes on a trip, it quickly spirals into a living nightmare for Gyuhwan. Seongbin inevitably begins harassing him, but Gyuhwan finally finds the courage to resist. However, his bravery is short-lived, and he flees into the woods, with an enraged Seongbin close behind. After falling off a cliff, Gyuhwan stumbles upon a strange shotgun and a box of 30 bullets, which, in his desperation and exhaustion, he intends to use against his classmates and their apathetic teacher. Back at the camp, the class talent show turns sinister. Something unnatural creeps in from the shadows, and as people begin transforming into twisted, bloodthirsty monsters, it seems that only Gyuhwan's mysterious shotgun can truly finish them off.