Two elite National Security System (NSS) agents, Hyeong-jun (Byung-hun Lee) and Sa-woo (Jun-ho Jeong), who ...
Two elite National Security System (NSS) agents, Hyeong-jun (Byung-hun Lee) and Sa-woo (Jun-ho Jeong), who were sworn blood brothers, both fall for fellow agent Seung-hee (Tae-hee Kim). Sa-woo attempts to suppress his feelings for Seung-hee and wishes the couple the best.
Hyeon-jun is then sent off on a solo mission to Hungary. In Hungary, Hyeon-jun accomplishes his mission and while in escape mode becomes wounded. Shortly later, Hyeon-jun finds out that he was betrayed by fellow agent Sa-woo. Seung-hee attempts to help Hyeon-jun escape, but a car explosion separates the two and both are misled to believe that the other person are dead. Hyeon-jun is then saved by an unknown voice and learns of the secret society "IRIS".
One year later, Hyeon-jun returns to Korea to seek revenge. During this time, the two Koreas are set to reunify, while the group "IRIS" are intent on stopping the reunification.