Joong-dong (played by Jung Joon-ho) was dispatched by his superior to be an undercover agent in a triad organization for many years to carry out a special mission. Meanwhile, Lee Yu-chan (played by Jung Woong-in), originally a small fry in the organization, secretly infiltrated the traffic police force as a "mole" because of his college degree. As fate intertwined, both gradually lost their way in the identities initially assigned to them, and thus began an epic espionage battle between the police and the triad...