Yi "Shioon" Shi-Woon's everyday life at Nine Dragons High School—which consists of beatings from fellow student Chang-Ho and his gang—is far from ideal. But one day, a mysterious man named Han Chun-Woo spots one of these beatings and, instead of offering support, brands Shioon a coward for refusing to fight back, adding insult to injury. To Shioon's surprise, he finds out that Chun-Woo is the new substitute English teacher at his school.

Tired of the daily abuse, Shioon decides to enroll at a martial arts academy to learn how to defend himself. On the way there, he stumbles upon Chun-Woo in a predicament—cornered in an alley by a group of angry men! Provoked, Chun-Woo suddenly dispatches them using martial arts techniques, which Shioon covertly records. Later, he uses this recording to blackmail Chun-Woo into teaching him to defend himself. Reluctantly, Chun-Woo agrees, and Shioon is soon thrust into the world of martial arts, known as Murim. However, Shioon is naive and unaware of his master's shady past and the unseen underbelly of society. How will Chun-Woo manage to teach Shioon and help him survive in the world of Murim?