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.