Choi Baekho suffered through years of bullying until he reached his breaking point. He wakes up with blood on his fists and gaps in memory, having taken down his tormentors. He's now known as Shinheung High's "reckless dog" and targets those who rely on numbers. However, his attempt to take down 11th-grader Do Changsoo gets him in trouble with the mob. In order to survive, he must team up with his rival and learn to control his aggression to become the worst nightmare for bullies.