Four close friends, Yong-bi, Ji-gong, Sang-woo, and Doo-man, who have just reached the age of twenty, embark on a journey to Pohang, a coastal town. This trip is in honor of Sang-woo, who is set to join the marine corps the following day. On the eve of Sang-woo’s departure, they encounter an event that alters their lives forever. The friends find themselves in a situation that is beyond their control, leading them through an unforgettable and irreversible day.