Lee Ji-hwan (Cha Tae-hyun) receives photographs in the mail that reminds him of how he met two girls, Shim Soo-in (Son Ye-jin) and Kim Gyung-hee (Lee Eun-ju), one summer five years ago. He shares his memories with his friend Chul-hyun (Park Yong-woo). He recalls initially being in love with Soo-in, but she rejects him. Throughout the summer, the three remain friends. Ji-hwan and Gyung-hee develop feelings for each other but are reluctant to admit it. Ji-hwan recalls the complex relationship between the three to Chul-hyun.