Cha Do Hyun (Ji Sung) experienced a series of tragedies as a child that left him an orphan, but he seemingly grew up fine overseas into an unfailingly nice young man. A violent confrontation one day, however, awakened another personality within him: the reckless, violent and volatile Shin Se Gi. From that day on, Do Hyun has struggled with the different identities that share his mind and body, and leave him in various outrageous predicaments when he regains consciousness with no memories of what occurred before. At the bidding of his cold grandmother, Do Hyun is forced to return to Korea and join the family business, all while keeping his condition a secret. He enlists the help of first-year resident Oh Ri Jin (Hwang Jung Eum), whom Se Gi harbors an immediate liking for. As Ri Jin grows closer with both Do Hyun and Se Gi, they begin to uncover the root of Do Hyun’s trauma and her past connection with them.