Do Kyungsoo, a petite boy with short-term memory loss gets lost one day when he was out with his best friend, Jongin. The boy was nowhere to be found and Jongin blamed himself every single day for letting Kyungsoo out of his sight. The worst part? He never got to confess his love for his "best friend". What happens when Kim Jongin, after searching for Do Kyungsoo for 3 years, finally finds a lead that could determine the whereabouts of the lost boy?