Sang Won, a architect who lost his wife in a sudden accident, moves to a new house with his daughter Yi Na in an attempt to rebuild their estranged relationship. Sang Won tries to connect with Yi Na, but their relationship barely improves. One day, Yi Na tells him that she has made a new friend, and she starts to become cheerful. However, strange noises start coming from Yi Na's closet and she begins to exhibit abnormal behavior. Shortly after, Sang Won starts having bizarre dreams and his daughter suddenly goes missing. While searching for Yi Na, Sang Won receives a call from a mysterious man named Kyung Hoon, who reveals that Yi Na is not the first person to disappear and that he has been searching for the other 32 missing children for the past 10 years. Sang Won and Kyung Hoon then join forces to find Yi Na and unravel the mystery behind the missing children.