After losing his wife in a traffic accident, Architect Sang Won and his daughter, Yi Na, move to a new house attempting to restore their estranged relationship and mentally heal. As soon as they arrive, Yi Na, who hardly spoke to her father, suddenly becomes cheerful, saying that she got a new friend and starts acting abnormally. Not long after that, Yi Na mysteriously disappears from the house and after a monthof searching, people start suspecting that Sang Won might have killed her.
After seeing their story on TV, a mysterious man called Kyung Hoon approaches Sang Won, telling him that Yi Na is not the first one to disappear, and that he has been investigating the disappearance of 32 other children that went missing under the same circumstances for the last 10 years. Sang Won and Kyung Hoon then join forces to find Yi Na and solve the mystery of the missing children.