1983: Ji-Hwan (Cho Jung-Seok) is a music teacher and he is soon to wed his girlfriend Yoon-Jung (Lim Soo-Jung). Yoon-Jung becomes involved in a case and Ji-Hwan attempts to protect her.
2015: Detective Gun-Woo (Lee Jin-Wook) and Ji-Hwan happen to see their daily lives through their dreams. Gun-Woo learns about a case that took place in the past from Ji-Hwan. Gun-Woo also meets So-Eun (Lim Soo-Jung) and, together, they go after the case that took place in the past.
Filming began October 1, 2014 and finished February 1, 2015 in Jongno, Seoul, Korea. The last scene filmed is set in the present day and involves the first time Gun-Woo (Lee Jin-Wook) sees So-Eun (Lim Soo-Jung). They meet during a New Year’s Eve celebration. About 200 extras gathered for that scene.