Hae Sung and Jung Won are ordinary high school seniors who are getting themselves ready for life after graduation. One day, Hae Sung wakes up to find everything surrounding him different. He was dead for 12 years.

Hae Sung looks for ways to figure out what happened to him when he accidentally runs into his high school friend, Ho Bang. Ho Bang visits Hae Sung's tomb every year with the rest of Hae Sung's high school friends. It turns out that Hae Sung was killed on his birthday.

Jung Won is confused and pressured by Min Joon's confession. Hae Sung finds out how his family and friends have been living through Ho Bang, who also tells him that he and the rest of their friends lost touch with Jung Won.

Jung Won takes care of Hae Sung who was injured and lost consciousness. Jung Won thinks she's insane for thinking that Hae Sung has comeback from death. Hae Sung finds out how Jung Won's life has been difficult without him and is heart-broken.

Jung Won decides to let Hae Sung stay at her place. They spend a good time chatting about their past. The next day, Hae Sung finds a way to help both Jung Won and Hae Chul out of the gang's hands. Meanwhile, Hae Sung runs into Young Jun, but Young Jun asks her to keep his family status a secret.

Jung Won tells Min Joon that Hae Sung is her cousin, which doesn't make Hae Sung happy. On their way back home, Hae Sung and Jung Won decide to have a drink together for the first time. Hae Sung honestly tells Jung Won about how he feels about the current situation he is in.