Kim Cheol-soo (Sol Kyung-gu), who looks ordinary, is a skilled, brave and capable agent in the Republic of Korea, but in his daily life he disguises his identity, and even his wife Young-hee (Moon So-ri) knows nothing about his true identity. In front of his wife, he is an ordinary office worker who is submissive and has no aura. Cheol-soo carefully maintains a balance between danger and mediocrity. One day, the plane carrying Baekwu-jin, a North Korean representative who was about to attend the six-party talks, was shot down by terrorists. Because the meeting was of great importance and affected the signing of the agreement on the reunification of the North and the South and the abandonment of nuclear weapons, the South Korean side sent Kim Cheol-soo and his partners to Thailand to rescue Baekwu-jin's daughter Baek Seol-hee, who had rich experience in nuclear weapons manufacturing. At the same time, Young-hee, a flight attendant, flew overseas after quarreling with her husband. On the way, she met Ryan, a handsome man, but she didn't know that this man was the cold-blooded killer who assassinated Baekwu-jin. In Thailand, which is in crisis, Kim Soo-chul is experiencing severe tests from the country and family...