Mark (Ma Dong-seok), who works in a nightclub in Los Angeles, has always dreamed of becoming a world champion in arm wrestling competitions. He is persuaded by Jin-gi (Kwon Ryul), who claims to be his agent, to return to Korea to participate in the national arm wrestling competition. In addition to the competition, Jin-gi also gave Mark the home address of his biological mother, who was adopted to the United States since childhood, as a return home gift. However, Mark only met his sister Soo-jin (Han Ye-ri), whom he had never met, and her two children. With Jin-gi's help, Mark participated in an illegal arm wrestling competition. Faced with the strong enemies of arm wrestling monsters, with the support of his family, can Mark realize his dream of becoming a champion?