The professional assassin Sook-hee is supposed to avenge those who murdered her husband but is taken by the police afterward. She becomes unconscious and wakes up at the national security service. They have seen her skills and want her to take work for them by doing top-secret assignments for them. At first, she refuses but realizes that she has to accept their offer in order to survive. Sook-hee, or Yeon-soo, who is her new name falls in love and starts dreaming about a family together with Hyun-soo. But she gets a new assignment on her wedding day that will change her life forever.