Tunnel is a 2017 Korean Drama starring Choi Jin-hyuk, Yoon Hyun-min and Lee Yoo-young. It aired on OCN and proved a hit.
Park Kwang-ho is a criminal sergeant detective in Hwayang Police Station in 1986. While pursuing a suspect through the titular tunnel, he is knocked out. When he comes to, he ends up in 2016, and has to use new technology and friends in order to solve the old case which remained cold, as well as fresh new cases.
Tunnel provides examples of:
- Alas, Poor Villain: After seeing the way Jung was treated by his mother, the detectives feel a slight twinge of pity, though they quickly shrug it off cause he murdered a lot of people.
- Arc Villain: Many, since the team solves many cases in 2016. Among them, Kim Tae-soo, Noh Young-jin and Kim In-hwan.
- Asshole Victim: Choi Hong-seok, who beat to death the teacher's son in the military and never felt remorseful, instead thinking upon the incident with glee. His head is bashed in with a rock.
- Big Bad: Dr Mok, who is actually the true mastermind behind the Dot Murders in 1986 and started murdering again in 2016.
- Big Bad Friend: Dr Mok, the actual killer and Seon-jae's mother's murderer, has been a friend and helper for Seon-jaw's cracking of other cases, which shocks and angers Seon-jae.
- Big "WHY?!": Due to desperation to go back to 1986, Park has this reaction regarding being transported to 2017.
- Chess Motifs: Done frequently with Dr Mok, who fittingly treats everything like a giant chess game. At the end, he finally gets a checkmate.
- Closed Circle: The rest stop during a storm becomes a setting for murder, and Kwang-ho and Seon-jae are stuck there trying to figure out who the murderer is.
- Contrived Coincidence: By a curious quirk of fate, all of the main characters are somehow related to one another. Seon-jae is actually the son of a 1986 murder victim Kwang-ho had interacted with in the past, and Jae-yi is actually Yeon-ho, the daughter of Kwang-ho and Yeon-soo.
- Cowboy Cop: As a reckless 80s cop (back when abusing suspects wasn't off the table), Kwang-ho is this.
- Dark and Troubled Past: Many of the perpetrators, including Jung, who's revealed to have lost his mind sometime ago and murdered all the dogs in his town as a high school student.
- Dies Wide Open: Many of the victims, which is justified since they died via asphyxiation.
- Driven to Suicide: One of the victims whose identity was stolen does this due to mounting debts in the millions which she wasn't even responsible for.
- Earn Your Happy Ending: In the end, Kwang-ho manages to return to 1988 and live a happy life with Yeon-soo.
- Evil All Along: Dr Mok, responsible for the autopsies, is revealed to be the actual perpetrator of the 1986 Dot Murders and two new ones in 2016.
- Evil Cripple: Kim Tae-soo, who killed the 1986 Dot Murder survivor because she rejected him for being creepy, and his hand.
- Faux Affably Evil: Dr Mok. He hides his identity of being the actual murderer pretty well until he's found out by Park Kwang-ho.
- Fish out of Temporal Water: Park Kwang-ho, who initially still believes in 1986, and not noticing the infrastructural changes, handcuffs an actual detective working there.
- Green-Eyed Monster: Kim Mi-soo, a waitress at a high-end restaurant, took the identities of several women in order to ruin their marriages and life after she herself broke up.
- Happily Married: Kwang-ho and Yeon-soo until Kwang-ho accidentally ends up in 2016 via the titular tunnel.
- Heartwarming: When Jeon and Kwang-ho finally recognize each other in the fourth episode.
- He Knows Too Much: The reason Dr Mok eliminated the second Park Kwang-ho, and pursued him all the way into a forest before strangling him to death.
- Hired to Hunt Yourself: In a rather twisted, ironic way, Dr Mok helps conduct autopsies and provides theories for the people he killed himself and is actually trying to justify them.
- Internal Reveal: That Kwang-ho actually came from the past, which is why the chief has been calling him Senior and why he knows all about the 1986 case.
- Joggers Find Death: Played oh so very straight. Most of the bodies uncovered are found by joggers, as is the second Park Kwang-ho's car.
- Left Hanging: Ultimately, Kwang-Ho returns to his own time - but does so with extensive knowledge about various crimes that would enable him to prevent most of them.
- We never get to know whether Kwang-Ho caught Mok in the past or not. Assuming he does, a lot of people would still be alive, including the other Kwang-Ho.
- What happened to Jung - after all, him becoming a serious problem happened after his extensive stay in the asylum; which was his mother's doing.
- Kim Young-ja, the fifth victim who survived her ordeal, ultimately dies at the hand of another guy - also something that might be prevented by Kwang-Ho's interference.
- And it's never made clear whether the 2017 Kwang-Ho left behind is a separate timeline or gets overwritten by his return (and presumably his subsequent changes to the timeline) to 1987.
- The Lost Lenore: Kwang-ho initially believes Yeon-soo is this after learning she died in a car crash, but he realizes he can go back in time, and since they're together, the car crash would never have happened.
- One-Steve Limit: There are exactly two characters named Park Kwang-ho. Both are related to the case, but one dies, allowing the other to take the identity for a while.
- Our Time Travel Is Different: The tunnel itself, which works strangely as it only sends one man into the future / past and at a convenient time in the case.
- Sanity Slippage: Jung Ho-young, who becomes insane thanks to his mother and kills dogs before moving on to humans after being inspired by the Dot Murders.
- Self-Made Orphan: Dr Mok killed his mother when he was young due to her always going out and servicing other ... people.
- Serial Killer: The main case they have to solve is the Dot Murder in 1986 and a new series of killings occuring in 2016.
- Teeth-Clenched Teamwork: Initially, Kwang-ho and Seon-jae get by with this. Once Seon-jae finds out the truth, their relationship gets better.
- Those Two Guys: Tae-Hui and Min-Ha.
- Time Machine: The tunnel seems to be a plot convenient one, helping the Detective get to 2016 to solve the case in order to go back to the past.
- Time Travel: The main plot of the series involves this as a detective from 1986 is sent into 2016 to solve the case.
- Wham Shot: After yet another young woman is killed the camera pans around to reveal none other than Dr Mok.
- Would Hurt a Child: The robber Noh Young-jin very willingly sticks a knife in Yoon Dong-woo for admitting to the police.
