Busan, 1998. Park Sae-ri, a high school student who has vowed never to ask a guy out again, decides to break her rule for the sake of the school's hottest guy, the guy that almost all the girls have a crush on. To such a responsible step must be thoroughly prepared, namely - to straighten unruly curly hair. The only salon that will do it with a guarantee is Park Yoon-seok's mom, the girl's new classmate who recently broke his leg and almost drowned. Sae-ri starts helping Yoon-seok in exchange for a free hair straightening treatment.