Lee Ji-hwan receives photographs in the mail that reminds him of how he met two girls, Shim Su-in and Kim Gyeong-heui, one summer five years ago. He shares his memories with his friend Cheol-hyeon. He recalls initially being in love with Su-in, but she rejects him. Throughout the summer, the three remain friends. Ji-hwan and Gyeong-heui develop feelings for each other but are reluctant to admit it. Ji-hwan recalls the complex relationship between the three to Cheol-hyeon.