After their parents' divorce, twins Baek Do Ha (Lee Jae Wook) and Baek Do Yeong (also played by Lee Jae Wook) were separated: Do Ha lived in the United States with their mother, while Do Yeong lived in Korea with their father. Do Yeong moved next door to Song Ha Gyeong (Choi Sung Eun), a girl around the same age as him. When Do Ha visited during the summer, the three kids spent time together, often watching the stars. As they grew closer, Ha Gyeong began to develop feelings for Do Ha, but felt that she couldn't confess her feelings out of fear of disrupting their group dynamic. As they go through college and their early careers, they fall out of touch... until tragedy strikes, and Do Ha must tell Ha Gyeong a painful truth that might tear them apart for good – or bring them closer than ever before.