An ardent animal lover and skilled veterinarian, no one would suspect Kim Soo Hyun (Chang Ki Yong) is actually one of the world’s deadliest men. Using his cover as champion of the small and furry to hide his true identity, Kim Soo Hyun has made a name for himself amongst the lowest of the low as the epitome of precision, skill, and above all else, anonymity. A mystery in and of himself, he is nothing more than a ghost, a shadow, a lethal whisper, hired by individuals and organizations the world over, to take care of problems only he is qualified to handle. On the opposite end of the spectrum, Do Hyun Jin (Nana) is the hard-working detective whose icy exterior hides a sympathetic soul. Using an effective combination of skill and instinct, Do Hyun Jin finds herself working a case that leads her straight to Kim Soo Hyun. Believing him to be the serial killer she’s after, Do Hyun Jin digs deeper into Kim Soo Hyun’s identity and his past but what she finds shakes her to her very core. Now tied by fate, Do Hyun Jin and Kim Soo Hyun set out to unravel the mystery that bound them years ago.