Onew, Jonghyun, Minho and Taemin had an already normal life without Kibum, after his disappearance five years ago. 

One day, Taemin found himself lost in a dark street and got into a fight. After defeat he was helped by a boy, who took him home to treat his wounds. There he met the boy's "family" and found someone that seemed familiar to him - Kibum, now known by Key. After the other refused his identity to Taemin, the last one left and was drived to his friends' house and despite what Kibum said, he told them that he found their childhood's friend. 

The boys want to know what caused him to disappear and begin their journey to win him back.