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Series / Signal

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Signal is a Korean crime drama series starring Lee Je-hoon, Kim Hye-soo and Cho Jin-woong that aired on the TvN channel from 22 January 2016 to 12 March 2016. A critical and commercial success, the drama became on the highest rated Korean drama series in Korean cable television history.

The story revolves around Lt. Park Hae-young, a profiler who hates cops after they ignored what he had to say regarding two criminal cases during his childhood. One of them was the kidnapping and murder of a classmate, an event that he witnessed and tried to inform the authorities of, but was ignored. As the statute of limitations of the kidnapping case comes close, Lt. Park discovers an old walkie-talkie, getting a message from a detective who gives crucial information with regard to catching the culprit.

After this incident, in response to the protest against the statute of limitations, the Korean government lifts that policy and a cold case squad is formed.

As he works his way around these mysteries, Lt. Park realizes that on the other end of the walkie talkie is a detective from the past named Lee Jae-han, who is missing in the present. After initial disbelief over the whole situation, the two work together in solving said cold cases by giving each other information from the past and present.

The cold case squad in the present, led by Detective Lee's junior, Cha Soo-hyun, earns recognition and face difficulties solving many unsolved crimes.

A Japanese version based on the show has aired on Fuji TV under the same title in 2018. A Thai version, known as 23:23 Signal, aired in 2023.

This show provides examples of:

  • Abandoned Hospital: Jae-han is lured to an abandoned mental hospital, where he finds the body of the supposed kidnapper. He's then clubbed over the head. It is even spookier when Hae-young arrives there 15 years later in response to the mysterious walkie-talkie transmission, and finds the place not only still abandoned but now covered in cobwebs of disuse.
  • Above Good and Evil: Kim finally gives Jae-han an abbreviated Motive Rant in episode 14, where he tells Jae-han that no matter what the cops do, the Crapsack World never changes, so they might as well use it to get rich.
  • Action Girl: Detective Cha Soo-hyun. In a fight, she's more than capable of holding her own.
  • Agonizing Stomach Wound: In the climax, Hae-Young gets one after he gets shot Taking the Bullet for Cha Soo-Hyun.
  • Almost Dead Guy: Episode 12 begins with Hae-young finding Commander Ahn gut-stabbed in the woods outside the hospital. He has just enough time to tell Hae-young that he killed Lee Jae-han, before he dies.
  • Anachronic Order: Due to the nature of the story with Jae-han and Hae-young talking to each other over the decades via the Portal to the Past walkie-talkie. The series jumps back and forth between the present day of 2015 (where Hae-young and Soo-hyun are investigating cold cases), 1989 and Jae-han's involvement in the South Gyeonggi serial killer case, 1995 and Jae-han's initial friendship with Soo-hyun, 1999 and the Inju gang rape case, and 2000 and the kidnap-murder of the the little girl.
  • Anguished Declaration of Love: Soo-hyun finally spits it out in episode 14 when she is riding along in the ambulance that is whisking Jae-han to the hospital after he got stabbed. Her "I like you...I like you a lot," followed by a lot of Inelegant Blubbering where she says it's OK if Jae-han can't get past his lost Lenore, makes both Jae-Han and the ambulance driver uncomfortable.
  • Arc Words: "Never give up."
  • Artistic License Law: While the statute of limitations in Korea was indeed removed for murder in 2015, it had already been extended from 15 to 25 years for first degree murder in 2007.
  • Aspect Ratio Switch: Uses 16:9 for present scenes, while using 21:9 with Anamorphic for past scenes.
  • Blackmail Backfire: Jung Kyung-soon, Lee Chun-goo's co-worker at the bus company, knew his son was the killer and blackmailed him for 15 years. When the statute of limitations was repealed in 2015, she decided to start blackmailing him again, and this time he killed her instead.
  • Bolivian Army Ending: The last episode ends with Senator Jang's goons storming into the hospital where Jae-han has been hiding out for years—but Hae-young and Soo-hyun are on the way.
  • Bittersweet Ending: Several storylines have a somber end even when the case is solved.
    • In the first arc, the culprit of the kidnapping case is arrested for the murder of a man who knew of her crime, but the statute of limitations for the abducted girl's death has passed and can't be prosecuted, much to the despair of the mother. These events lead to a backlash against the statute of limitations, causing the government to repeal the policy on unsolved murders, leading the formation of the Cold Case Squad.
    • Lee Jae-han manages to clear the name of an ex-con who was framed by the real culprit, preventing Cha Soo-hyun from being indirectly killed by him in the present. The ex-con however, is arrested anyway for murdering a man he blames for his daughter's death in a bus explosion and dies in prison.
  • Big Brother Worship: Hae-young idolized his brother Sun-Woo to a big extent. The flashbacks show us that Sun-woo was a really good brother and person and completely deserving of Hae-young's love and affection.
  • Butterfly of Doom: Both Jae-han and Hae-young learn the hard way that actions have consequences, especially when it comes to the past.
    • After learning of the location of the next crime scene from a serial killer from Lt. Park, Detective Lee is able to save the victim, sees the culprit and catches him...or so he thinks. While the victim managed to survive and have a family, the person that Detective Lee arrests (who happened to be wearing the same outfit as the killer) dies in custody when the chief becomes too aggressive. The murders of the next two victims also occur much sooner, with another person killed with the same MO in the present time.
    • After learning that a burglary case would remain unsolved in the present time, Detective Lee asks for some tips, which Lt. Park gives. He ends up arresting an ex-con that he befriended, but as a result, the ex-con's daughter, who saw Lee as an uncle, dies in a bus accident.
    • In a case about serial killings with the victims asphyxiated, which has nine victims, Detective Lee manages to catch the culprit sooner despite Lt. Park refusing to give any information. This trope is subverted in that nothing wrong seems to be apparent, with future victims being still alive in the present, though Lt. Park thinks something bad could have happened and he just doesn't know what it is.
  • Call-Back: The Time Passes Montage of Hae-young's troubled youth in episode 1 shows him getting into a fight in a pool hall. Episode 12 reveals that he was in the pool hall confronting one of Sun-woo's classmates, the one who gave false witness and told the cops that Sun-woo took the victim of the Inju gang rape on a bus.
  • The Cavalry Arrives Late: Even with Hae-young's warning, Jae-han is too late to stop Sun-woo's murder on February 18, 2000.
  • Chekhov's Gun:
    • Lee Jae-han's old notebook, which contained the memo about his unsolved cases. He uses it in the last episode to send a message via The Slow Path to Hae-young in 2016.
    • The stun gun that Jae-han gave his sweetheart in 1989. It didn't save her, but it did result in the apprehension of the killer in 2015 when the cops recovered it and found Jin-hyung's DNA.
  • Cobweb of Disuse: The abandoned hospital where Lt. Park goes in the first episode, which has been closed for at least 15 years. He finds a body there.
  • Company Town: It seems that Inju revolves around Inju Cement, which is why monstrous teen Jang Tae-jin gets away with orchestrating the gang-rape of a fellow student, and why the cops frame Sun-woo.
  • Cowboy Cop: Once Jae-han realises that most of the cops he knows cannot be trusted, he begins to take his own initiatives.
  • Creepy Souvenir: The killer in the suffocation cases kept trophies. Sometimes, the names were already on them, like one victim's diary or another's name tag from work. If they didn't already have a name on them, he labeled them.
  • Dead All Along: When he first talked to Detective Lee, Lt. Park searched for any members of the police with his name, only finding people with the same name and a file that says he's missing. After realizing the walkie-talkie communicates with the past, he does some digging and later finds his remains underneath a house. It is later revealed that Detective Lee was murdered by a crooked cop for having evidence of Lt. Park's brother being murdered by his boss.
  • Desk Sweep of Rage: Lee Chun-goo, the bus driver, does this in episode 4 when Hae-young confronts him with photos of the Gyeonggi serial killer victims. Chun-goo, who has claimed responsibility for the murders, is covering for the real killer, his son.
  • Disposable Woman: The majority of murder victims are mainly women, one of them being a child in the beginning.
  • Dirty Cop: Unfortunately, the series is liberally peppered with them. The biggest offender though is Kim Bum-Joo who rose to his current position by engaging in bribery, corruption and even murder.
  • Dramatic Gun Cock: A gun is dramatically cocked in episode 8 in the flashback scene that reveals that, yes, Deputy Chief Ahn was the one who murdered Jae-han back in 2000.
  • The Dog Bites Back: Sick of being his boss' whipping boy and haunted by killing Lee Jae-han, Ahn Chi-soo resigns and reveals that Park Hae-young is Sun-woo's little brother and offers to tell him everything. It gets him murdered. Before that, after learning that his daughter will die soon, he hides the evidence that Hae-young is related to Sun-woo.
  • Finger-Twitching Revival: Subverted in episode 16. Hae-young flatlines in the hospital, after he was shot. Then there's a cut to his Finger Twitching Revival...but he's not reviving, he's awakening in his bed at home, after actions in the past have completely changed the timeline that he's in.
  • Glasses Pull: The detective in charge of the 1989 investigation into the South Gyeonggi serial killings does this in episode 3, when Hae-young comes to ask. He then screams that everything that went wrong with that case was Jae-han's fault. (We later learn that Jae-han nabbed the wrong guy, who had a seizure and died after the cops slapped him around.)
  • He Knows Too Much: The reason Lee Jae-han met his end in the original timeline.
  • Heartbroken Badass: Jae-han, in a manner of speaking. Won-kyung's death spurs Jae-han into become a detective who will not rest until victims receive justice.
  • Inelegant Blubbering: Soo-hyun's Anguished Declaration of Love to Jae-han in episode 14 is accompanied by a lot of loud wailing and blubbering. Jae-han is caught completely off-guard.
  • The Killer Was Left-Handed: Hae-young's "Eureka!" Moment comes in the first episode when he remembers the coffee cup and and scissors and realizes that the killer is a lefty and their suspect, Nurse Kang, isn't.
  • Lonely Funeral: Due to Jae-han being remembered as a dirty cop, Soo-hyun, Hae-young, and Jae-han's father are the only mourners at his 15-years-delayed funeral in episode 13.
  • The Lost Lenore: Won-Kyung for Jae Han. He's never really able to get over it and the fact that he couldn't save her in time forever remains a source of grief.
  • Meet Cute: Episode 5 reveals that Jae-han and Soo-hyun met in 1995 when Soo-hyun, a gung-ho rookie, was admitted as the first woman in their unit. The other cops frantically remove their hanging underwear and nudie pictures from the break/nap room, but Jae-han, sleeping on the floor, refuses to move. He tells Soo-hyun when she enters that all cops are one gender.
  • My Greatest Failure:
    • The four cold cases that the Cold Case squad is tasked with solving are all cases that Lee Jae-han considered his greatest failures either because he could not catch the culprit right away or because he was he was thwarted by other factors.
    • In a way, this also applies to Park Hae-Young - that he refused to join Yoon in the rain back when he was a kid (and thus inadvertedly lead to her going with her murderer) has left a deep mark on him.
  • Near-Death Experience: All the three leads have near death experiences during the course of the drama. Cha Soo-hyun almost becomes the victim of a serial killer. However, she is able to escape in time and is luckily found by Jae-han. Park Hae-young takes a bullet for Cha Soo-hyun and comes close to losing his life. Lee Jae-han survives an attempt on his life by Kim Sung-bum, Kim Bum-joo and Ahn Chi-soo. Luckily for him, he's able to call his team for back-up and they arrive in the nick of time.
  • Never Suicide: Hae-young finally finds out in episode 14 that his brother Sun-woo was murdered to stop him from revealing the truth about the Inju rape case.
  • Nice Job Fixing It, Villain: Discouraged by the detrimental changes they've made to the timeline, Park was just about to stop looking into Jae-han and taking his calls for good and it would also have stayed that way had Ahn Chi-soo abstained from pulling him back in.
  • Oblivious to Love: Back in 2000, Jae-han is the only person at the police station who has no idea that Soo-hyun is in love with him. The other cops laugh about this and boggle over how two years have gone by and he still hasn't figured it out.
  • One-Word Title: Signal
  • Perfumigation: A throwaway gag after Jae-han and Soo-hyun go out on their one and only date in episode 16. Soo-hyun's little sister, who is desperate to get Soo-hyun married off, tells her to use some perfume, which Soo-hyun does reluctantly. At the restaurant, Jae-han asks what that weird smell is, to Soo-hyun's mortification.
  • Police Are Useless: Lt. Park's reason for his grudge against them. He has a point, considering how the cops blew him off back in 2000 when he witnessed the kidnapping, how they railroaded his brother, and how the Seoul police are ridden with corruption from top to bottom.
  • Portal to the Past: Much like Frequency, it can only transmit sound. And it's just the one radio, in different time frames: Hae-young gets ahold of Jae-han's old walkie-talkie in 2015 and uses it to communicate with Jae-Han, holding the same walkie-talkie in time frames from 1987 to 2000.
  • Posthumous Sibling: Park Sun-Woo, older brother to Hae-young, dead 15 years. The mystery of his death plays a big role in the second half of the drama.
  • Product Placement: Park Hae-young eats at a Subway in episode 11. They even get in a shot of the menu.
  • The Profiler: Park Hae-young himself. While he is good at deductions, he also stresses that it is not an exact science.
  • Promotion to Parent: Sun-woo took care of Hae-young like a parent would, because their parents were often not around.
  • Rape as Drama:
    • A high school gang rape case is a major part of Lt. Park's backstory, as his older brother was wrongfully convicted of instigating an assault on a classmate.
    • A woman who faked her death reveals that she was a victim of this.
  • Revisiting the Cold Case: The premise of the series.
  • Ripped from the Headlines: Some of the cases have similarities to real life cases in Korea, which were also dramatized in other media:
    • The kidnapping of Kim Young-joo, Lt. Park's classmate, seems to be inspired by a real-life abduction of nine-year-old boy in 1991. Despite 87 ransom calls from the kidnapper to the child's parents asking for ₩70 million (US$75,000), Lee's dead body was found in a ditch near his home 44 days after he went missing; the killer was never caught, and the 15-year statute of limitations on the case expired in 2006. This incident was the basis for the Korean film Voice of a Murderer.
    • The cold case squad's first assignment after its formation is basically the Hwangseong murders with a different case name, which Memories of Murder was based on. It is also chronologically Lee Jae-han's first time communicating with Lt. Park.
    • The Korean 15-year statute of limitations for murder was in fact repealed in 2015.
  • Ripple Effect Indicator:
    • Both the notes in Hae-young's notebook, and the notes he's written on a whiteboard in the squad room, change when his communication into the past leads to Jae-han saving the eighth victim of the serial killer in 1989. As Hae-young stares in astonishment, the notes on the eighth victim change from murder to attempted murder.
    • Later, one of the cases on Jae-han's unsolved cases memo disappears, after Hae-young's help leads to Jae-Han solving the case after all.
    • There's usually a puff of wind, even indoors, when the past has been changed somehow.
  • Ripple-Effect-Proof Memory:
    • Hae-young's memory remains unaffected when his communication into the past changes the past, and Jae-han saves a victim of a serial killer. Park is the only only one who remembers that in the past (that is, in the original, alternate past) that particular woman was in fact murdered.
    • Soo-hyun's memory was not ripple proof, until the last episode, where she's zapped into a new timeline when the future resets, but still remembers the history before that reset, namely everything with the cold case squad (which in the new present, Hae-young never joined) and Hae-young getting shot in the parking garage. Why her memory became ripple-proof is not justified, although it may be that she used the walkie-talkie to communicate with Jae-han in episode 15, and so became part of whatever A Wizard Did It magic is going on here.
  • Rooftop Confrontation:
    • The first serial killer arc ends in episode 4 with a rooftop confrontation between Lee Jin-hyung, the killer; Lee Chun-goo, his father, and Detective Lee Jae-han. Jin-hyung winds up falling off the roof which is why he's a paraplegic in 2015.
    • There's another one in episode 14 when the cops chase a random bad guy onto a roof, Soo-hyun in the lead. The bad guy pulls out a knife and is about to stab her when Jae-han shows up on the roof and tackles him. He winds up getting stabbed instead, but not fatally.
  • Serial Killer: Two of the cold cases the squad is asked to solve deal with serial killers, one of them already mentioned above.
    • A later case reveals that multiple murders by asphyxiation took place in a small town right under the authorities' noses from 1990 to the present.
  • Screw the Rules, I Have Money!: A running theme that Lee Jae-han comes up against many times in the past. The perpetrators in two cases are boys who are wealthy and well-connected.
  • Shoot the Rope: The serial killer in episode 11 is trying to hang himself in the woods when Detective Cha saves him by shooting through the rope.
  • Slipstream Genre: In 2015 a young detective stumbles across a vintage walkie-talkie, which, somehow, allows him to communicate 15-25 years into the past with the previous owner of that same walkie-talkie.
  • The Slow Path: Jae-han uses this in the last episode. On the run from Senator Yang's goons in the year 2000, he leaves the incriminating floppy disk in the possession of Hae-young's mother, then leaves a cryptic note in his notebook, which he knows Hae-young will later find. Hae-young finds the note in 2016, goes to his mom's house, retrieves the disk that's been waiting there 16 years, and uses it to bring down Senator Jang.
  • Split-Screen Phone Call: Used in episode 3 when Hae-young and Jae-han are communicating with each other over a 26-year gap via walkie-talkie.
  • Spoiled Brat: Many minor characters are rich kids who think they can get away with anything because they have rich fathers backing them.
  • Stable Time Loop: Episode 15 finally explains why, way back in Episode 1, Jae-han had that note to go to Seonil Mental Hospital on August 3, 2000. It's because Detective Cho, after she found out about the magic walkie-talkie, called him from 2015 and warned him not to go there on that date.
  • Staggered Zoom: Done in-universe when Section Chief Ahn, who is obviously up to no good and is suspicious of Hae-young, finds the security cam footage of Hae-young discovering the magic walkie-talkie in the bag of junk. He fiddles with the controller and does a staggered zoom in on Hae-young's grainy, black-and-white face.
  • Taking the Bullet: Played straight as straight can be as Hae-young leaps in front of Soo-hyun and takes a bullet meant for her, at the end of episode 15.
  • Turn in Your Badge: Back in 1989 in episode 3, Jae-han has to turn in his badge and, worse, his walkie-talkie, when his superiors grow suspicious of his strange knowledge of the killer's activities.
  • Vigilante Man: Jae-han went after Chun-goo the bus driver in episode 4, believing that Chun-goo killed his sweetheart but not having any evidence. When Chun-goo's son Jin-hyung shows up wearing the killer's black hoodie outfit, Jae-han realizes that he is the killer, and chases after him with a gun. It ends with a Rooftop Confrontation.
  • We Can Rule Together: In episode 14 Kim finally drops the pretense and says that Jae-han is a smart guy and that he should join Kim's empire of corruption. Jae-Han refuses, saying that Kim would just use him and abandon him, as seems to be happening with Kim himself and Senator Yang.