15 years ago, Yoon Jae-ha (Seo Do-young) followed his family to an unknown island. The unfamiliar environment and the island with nothing made Jae-ha very depressed. At this time, he met the girl Seo Eun-young (Han Hyo-joo). The clever Eun-young would use shells and other things to make Jae-ha happy. The childhood sweethearts spent a wonderful time on the island, but later lost contact for various reasons. It was not until they met again in Austria, the hometown of waltz, that they met again. However, what followed was not joy, but hesitation with a lot of thoughts in their hearts. Jae-ha became a well-known pianist, but he was withdrawn and had only one friend, Billy (Daniel Henney), who was his agent. Hyo-joo won an award for her handicrafts and had the opportunity to come to Austria for further study. The two people with different identities were able to renew their relationship, and the record planner Song Yi-na (Lee So-yeon) also liked Jae-ha. The four of them composed a spring waltz in Austria...