Abandoned by his mother shortly after immigrating to America, Gon is raised by the mafia and grows up to become a cold-blooded hitman. Though usually flawless in taking out his targets, Gon makes a terrible mistake of killing an innocent young girl. A flood of guilt takes over his life and the situation becomes worse when his boss assigns him the job of killing the young girls mother. Gons new target, Mogyeong, is a risk manager at an investment firm and has buried herself in work to bury her grief. She is completely unaware of her role at the heart of a dangerous conspiracy. Finally, she meets the man who wants to tell her the truth behind the death of her child.