Tunnel

Detective Park Kwang Ho is unable to find leads on several murders with the same MO. Frustrated, he focuses more intently on catching the killer, worrying his coworkers.

Kwang Ho is shocked to find himself transported 30 years forward in time to 2016, where he assumes the identity of another police officer and starts work on a case with a new partner.

Kwang Ho is convinced he was sent to the future to solve the 30-year-old case, but clashes with his coworkers over a new unidentified victim.

Once Sung Shik figures out who he is, Kwang Ho asks him for help finding Yeon Sook. A burglary case leads to murder, and Professor Shin is brought in for an unusual request.

Kwang Ho and Seon Jae investigate a murder in a roadside rest area that brings up memories for Seon Jae. Kwang Ho learns that the officer whose identity he assumed is missing.

A stolen identity case causes Sung Shik to worry that Kwang Ho will be found out. Professor Shin looks into the Jung Ho Young case.

Soon Jae, believing him to be an identity thief and murderer, offers to help Kwang Ho investigate the other Kwang Ho, who is dead under mysterious circumstances.

Kwang Ho and Seon Jae agree to investigate the Jung Ho Young case together. The police team tracks down an arsonist.

With Jung Ho Young attracting the public’s attention and becoming bolder, the entire police station is ordered onto his case.

As the police scramble to pin down Jung Ho Young’s location, Professor Shin remains the only one who believes that he isn’t responsible for all of the murders and decides to take action.

The police search for more evidence to convict Jung Ho Young and unearth more mysteries. Kwang Ho cannot bring himself to tell Professor Shin who he really is.

As the police turn their attention to the second murderer, Kwang Ho begins to suspect Professor Mok, who has figured out who Kwang Ho really is.

Kwang Ho searches for sufficient evidence in the past while his friends in the present retrace his actions.

The police arrest Mok Jin Woo, hoping to get a confession before the 48 hours to produce evidence are up. Professor Shin investigates his past to find his motives.

Professor Shin stalls for time after being kidnapped by Mok Jin Woo, hoping that the police will be able to track him.

Series finale: Seon Jae struggles to hold onto his composure as the police again try to force Mok Jin Woo to confess.