Su Yeon is a former journalist and a current National Intelligence Service Agent. Chun Woo is an agent with the Foreign Intelligence Bureau where Jin Sook works as a deputy commissioner. The three of them each have their stories and secrets. Su Yeon, who used to be a cheerful and brave woman, closes herself off and takes a dark turn after her lover dies a year before. After she joins the NIS, Su Yeon faces various incidents. There is also a secret behind Su Yeon's past relationship with Chun Woo, the seemingly perfect and cold-hearted black agent. A case from four years ago is revealed, involving Jin Sook, the woman who managed to keep her position as the head of the Foreign Intelligence Bureau amidst power struggles, other female agents, as well as Su Yeon and Chun Woo.
