Seungmin (played by Uhm Tae-woong) works as an architectural designer in a construction company. One day, he receives a new house design project, and the client is Seoyoung (played by Han Ga-in), his dream lover from his student days. The two met in the architecture introduction class of the university many years ago. The 20-year-old Seungmin (played by Lee Je-hoon) fell in love at first sight with Seoyoung (played by Bae Su-ji), a girl from the music department who came to audit the class. The two became closer as they spent time together every day. However, the young Seungmin was shy and awkward at the time, and he could never express his love properly, which eventually led to the end of this beautiful first love. Many years later, Seungmin and Seoyoung's reunion made the old love shine again. However, the two are no longer the carefree students of the past, and Seungmin already has his own fiancée. Can Seungmin and Seoyoung continue their love from their youth?