This is the suspenseful story of a man who needs to kill and a woman who searches for him.
Kim Soo Hyun is a skilled contract killer who becomes a killer in order to find his family. Nobody in the public knows anything about Soo Hyun, including his age, name and race. Deep inside, he constantly looks for love, but struggles to develop and maintain any pure relationships around him.
Do Hyun Jin is a brilliant but arrogant detective working in Seoul, who graduated from police academy as the most excelled. Although she looks cold and stern on the outside, she is in fact a very sympathetic individual. Hyun Jin trusts her instincts and isn't afraid to rely on the things around her to make a decision to the best of her abilities. She lost her lover in an accident, and begins to chase after Kim Soo Hyun to reveal a mystery.