A perfect killer makes his first mistake... falling in love with his target.

A quiet, professional killer, Hyun-jun, arrives at a house to kill a man in his sleep, only to discover a woman alone under the sheets. Jin-young has decided to kill herself after a traumatic break up with her lover of seven years, but she wants to go out with a bang, not with a miserable and lonely dose of commonplace sleeping pills. The most extraordinary love story begins.