An endless vengeance of a mysterious lady who has been raised as a killer.
Sook-hee, a trained assassin, takes revenge on the men who murdered her husband. After losing consciousness, she awakes at the National Intelligence Service. The NIS wants her to undertake confidential missions, but Sook-hee initially refuses. However, Sook-hee decides to accept her new identity as Yeon-soo in order to stay alive. Under her new identity, she meets Hyun-soo, and they dream of starting a family. However, on the day of their wedding, she is assigned a new mission that changes everything.