Tunnel

Park Gwang-ho takes the serial murder case that only targets women in Hwayang city, 1989. Even though he has been working hard, the suspect does not leave any evidences; finally, Gwang-ho faces a suspect of a serial murder case in a tunnel.

Gwang-ho who has been chasing down the suspect suddenly moves to year 2017, after 30 years from his timeline. After visiting his police station, he becomes the youngest detective of the station; then, a dead body is found at Hwayang City.

Gwang-ho figures out the same mark from the dead body that has been leaved on the victims before, and is convinced that this murder case is on the same line of the serial murder case that happens 30 years ago, which is from his original timeline.

The head detective Seong-sik tracks down Gwang-ho's behavior since he suspects Gwang-ho; however, Seong-sik notices something that he cannot believe. Gwang-ho tries to find his wife 30 years ago, but cannot find her.

Finally, a dead body with seventh mark shows up; which means the serial murder is restarted. Gwang-ho and Seong-sik try to find the real Park Gwang-ho who was born in 1988 to figure out the reason that he comes to the future.

Gwang-ho from the past gets interested in a weird identity thief case that one woman reported. After that, Gwang-ho and Seon-jae get close together; however, Seon-jae gets suspicious due to Gwang-ho's weird activities.