Thirty-year-old Yun-woo bumps into a high school student in the elevator while on his way to work. His heart starts pounding at this teenager's boldness. At a subway station, KANG Sook can't stop staring at the long-haired, beautiful Ha-kyung. Ha-kyung breaks up with KANG Sook only a few hours after they first meet. However, KANG Sook has already fallen in love with her.