Two elite National Security System (NSS) agents, Hyeong-Jun (Lee Byung-Hun) and Sa-Woo (Jeong Jun-Ho), who were sworn blood brothers, both fall for fellow agent Seung-Hee (Kim Tae-Hee). 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.

Two elite National Security System (NSS) agents, Hyeong-Jun (Lee Byung-Hun) and Sa-Woo (Jeong Jun-Ho), who were sworn blood brothers, both fall for fellow agent Seung-Hee (Kim Tae-Hee). 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. [ Contract ]