When her son gets critically injured in a car accident, a mother discovers that there's more to his relationship with his friend than she had thought.

On the night that 17-year-old Dong-jun's only friend, Kang-hyeon, fell from a high place, Dong-jun made a choice that determined the direction of his entire life. Dong-jun's regrets and remorse following that choice made him experience life in three different universes. These are the various lives of the 42-year-old Dong-juns who live different lives in Seoul, Daegu and Busan 20 tears later.

As Tae-in moved away suddenly, Do-ha embarked on a long-distance relationship that certainly wasn't planned. Although they talk to each other daily and constantly through KakaoTalk and video chat, they all never enough in fully expressing his love for her. So he secretly plans to propose to her. But for some reason, Tae-in contacts him less and less often. Do-ha feels his trust and confidence in their love breaking down slowly...