With no memory of her parents or where she came from, Min Yuna lives in a girls foster home. The only piece of her birthparents is a lock necklace that has been around her neck since she was found in a dark alley as a baby. Now 16, Min Yuna hopes to find who she is...until she meets the school playboy, Taehyung, in which she is drawn to and doesn't know why. Will Min Yuna find the key to her lock, or remain lost forever?