Gao Shengxi (Lee Jun-ki) is a taciturn boy who likes to read and think. In fact, he is a master fighter who can beat seven people alone. Zhang Jiabi (Lee Moon-sik), an office worker, was determined to avenge his daughter because her daughter was bullied by a male classmate. He was usually timid and determined to avenge his daughter, so he found Gao Shengxi, hoping that Shengxi could teach him how to fight. After Jiabi begged hard, Shengxi agreed to be Jiabi's master. Next, Shengxi arranged a series of hard training, and various trainings emerged one after another. After 40 days of training, Jiabi was completely refreshed. The day of the decisive battle is coming. Can Jiabi defeat the powerful opponent to avenge his daughter?