In 1986, Park Gwang-ho works as a successful detective in an enthusiastic manner. However, his life changes when he takes the lead in a serial homicide case and passes through a tunnel while chasing the "culprit". He time travels 30 years into the future (2016), where he meets a new partner, Kim Seon-jae, an eccentric elite detective that has a high ability in investigation. When the serial killer continues the "modus operandi" of his murders that happened 30 years ago, the detective duo work together with criminal psychologist, Professor Shin Jae-yi, to solve the unsolved murders and to catch the murderer.
