Mi Kyung lives apart from her husband and raises Soo Hyun, her high school-aged son. One day, Soo Hyun brings home his friend Yong Joon to stay. A few years later, after completing his military service, Soo Hyun gets into an accident while on a trip with Yong Joon and is hospitalized in critical condition. Soon after, Mi Kyung discovers a secret her son and Yong Joon has been keeping from her.