Since she was a little girl, Sook-hee was brought up to become a deadly assassin. She gets a second chance in life when South Korea's Intelligence Agency's Chief Kwon recruits her to become a sleeper cell. "Work for us for 10 years, you'll gain freedom."Her new identity is Chae Yeon-soo, 27 years old, theater actress. With a promise of complete freedom after serving the country for 10 years, Sook-hee begins a new life. For someone who lived a life of a killer, living a normal life is no easy task. But when 2 men appear in her life suddenly, she uncovers secrets of her past...