A father (Ryoo Seung-Ryong), who is mentally handicapped, but loves his daughter very much, is falsely accused of a crime and sent to prison. Later, his daughter Ye-Seung (Park Shin-Hye, who is a law school student, works to prove his innocence.
Back in 1997, Yong-Goo lives happily with his daughter Ye-Seung (Kal So-Won), even though he has the intelligence of a child. They stop by a shop everyday to look at a yellow Sailor Moon backpack that he hopes to buy his daughter. One day, they notice that the last yellow Sailor Moon backpack is being sold. Yong-Goo goes inside the store to plead his case, but the father buying the backpack ends up slapping Yong-Goo.
The following day, the girl who bought the yellow Sailor Moon backpack sees Yong-Goo working in the grocery store parking lot. She tells him that she knows another store that sells the same yellow backback. Yong-Goo follows the girl to a traditional outdoor market. A short while later, the girl is laying on the ground unconscious and Yong-Goo is trying to perform CPR. A woman walks by and calls the police.
Yong-Goo is accused of kidnap and murder. The father of the dead girl is also the chief of the National Police Agency. Yong-Goo is given the death penalty and incarcerated. In prison, Yong-Goo shares a jail cell with five other inmates. One day, Yong-Goo saves the life of his cellmate So Yang-Ho (Oh Dal-Su) from a rival prison gang leader. So Yang-Ho then offers to help Yong-Goo in any way he can to return the favor. Yong-Goo tells So Yang-Ho that he wants to see his daughter Ye-Seung. The five inmates then plan to make a miracle happen.