Hyungjoon is a radio DJ, one day he is shocked by a letter delivered during a live broadcast, a letter from a familiar name. It is written by Jung Suok, his first love from 23 years ago, the love tucked away into a corner of his heart. As he reads the handwritten letter, old memories from all those years ago come to life.
The time is 1991, Bumsil and his friends gather at their remote island hometown for the summer vacation. The five of them are as one, and they embark on an unforgettable summer. Bumsil is willing to do anything for Suok. The two 17-year olds are headed for a moment that will never be forgotten.