Criminal profiler Park Hae-young (Lee Je-hoon) solves a kidnapping case involving a culprit who apparently disappeared after the crime with a mysterious walkie-talkie he picks up. The success of this case triggers the formation of a long-term cold case team, led by Det. Cha Soo-hyun (Kim Hye-soo), who has searched for her long-lost mentor, Det. Lee Jae-han (Cho Jin-woong), over the past 15 years. With the help of Jae-han, the person at the other end of the walkie-talkie, Hae-young solves other cold cases that had remained unsolved for years while also helping Jae-han help solve other cases. Unintended consequences due to the changes in the past follow.
In the summer of 2000, 10 year old primary school student Park Hae-young notices fellow classmate Kim Yoon-jung leaving school with a woman. Yoon-jung is later reported to have been kidnapped when her mother receives a ransom note. The suspect is a male medical student named Seo Hyung-joon identified by a thumbprint; Hae-young disbelieves that as he saw Yoon-jung left with a woman. After the ransom money is delivered, the corpse of Yoon-jung is recovered while Hyung-joon is never found. 15 years later and a few days before the statute of limitations on the case has passed, Hae-young becomes a criminal profiler while the Yoon-jung case remains unsolved. Hae-young chances upon an old police walkie-talkie and intercepts a live communication from a police officer named Lee Jae-han in 2000, who has discovered Hyung-joon's corpse. Jae-han is then attacked by an unseen assailant. Traveling to the same location in 2015, Hae-young finds the remains of Hyung-joon with his thumb removed. Police superintendent Kim Bum-joo attempts to bury the case after the press knows of the discovery of Hyung-joon's corpse, but Hae-young gives key details of the crime and suspect to the press. Presenting his theories before officer Cha Soo-hyun and lead detective Ahn Chi-soo, Hae-young proposes that the actual culprit is a woman who was a nurse due to her experience with a scalpel which was used to remove Hyung-joon's thumb. After Hae-young's press release was aired and a tip on the suspect came in. A nurse's locker is discovered containing a countdown on a calendar, legal books and shoes fitting the suspect's profile and the nurse was tracked down and detained by the police. Hae-young realizes that the nurse they detained is right-handed while the items in the locker belonged to a left-handed person. Fellow nurse, Yoon Soo-ah, is detained after Hae-young deduced she is the real culprit.
2
"We Still Have a Chance"
Kim Won-seok
Kim Eun-hee
January 23, 2016 (2016-01-23)
Soo-ah's blood is matched to Hyung-joon's glasses too late as Yoon-jung's statute expires, but after time of death is established for Hyung-joon, Soo-ah is arrested again and charged and convicted of that murder. Amid mounting public pressure, superintendent Bum-joo institutes a new cold case squad in Seoul, to be overseen by Chi-soo, led by Soo-hyun, and including fellow officer Kim Gye-chul and forensic scientist Jung Han-ki, with Hae-young as their criminal profiler. Their first case is the Gyeonggi Nambu serial murders, the most famous cold case in Korea. In 2000, then-rookie Soo-hyun bonds with the veteran detective Jae-han. Later, a seriously wounded Jae-han then communicates with Hae-young over the walkie-talkie again, leaving a cryptic message warning Hae-young that he will have to convince him in 1989 as "they" will start again, before a gunshot is heard. While looking up police officers named Lee Jae-han, Hae-young receives a sudden communication on the walkie-talkie from the 1989 version of Jae-han, who is part of the team investigating the then-ongoing Gyeonggi Nambu case. While in 2015 Hae-young is staring at photographs of the 8th and 9th Gyeonggi Nambu murders, in 1989 Jae-han walks along train tracks due to a key detail told to him by Hae-young of the 8th murder that has yet to happen. As Jae-han discovers the still living 8th victim, in 2015 all records of the Gyeonggi Nambu murders change.
3
"We Can Prevent the Killings"
Kim Won-seok
Kim Eun-hee
January 29, 2016 (2016-01-29)
In 2015, Hae-young realizes that everyone else's memory has changed to accommodate the new reality of the 8th victim, Lee Mi-sun, surviving the attack, but he alone remembers the events of the original reality. After talking to 1989 Jae-han on the walkie-talkie again, Hae-young realizes he is talking to Lee Jae-han who is in the past, and warns him of the next Gyeonggi Nambu murder. After meeting with Mi-sun's now existent daughter, Hae-young realizes that he can change the past. Later, while hoping to question Jung Kyung-soon, a coworker of the 8th victim, Hae-young and Soo-hyun discover her corpse as the new 10th victim of the Gyeonggi Nambu serial murders. As this reopens the case, it falls under the jurisdiction of the Gyeonggi police department and the cold case squad is pulled off the investigation. Hae-young attempts to prevent this death by using the walkie-talkie and Jae-han to catch the perpetrator in the past. In 1989, after discovering Mi-sun, Jae-han was attacked and chases down and arrests his attacker. However, the arrested man is an innocent bystander and dies of a seizure during custody, while the killer commits the 8th murder. Due to this, Jae-han is suspended from the police force and blames Hae-young, searching for him in a rage. In 1989 and 2015, Hae-young and Jae-han come to the same conclusion: that the killer was forced to board a bus to escape, and thus was seen by the other people aboard that bus. However, this theory is rebuffed by the bus driver Lee Chun-goo, who claims that no one boarded the bus at that specific stop. For interfering with the investigation despite no longer actively being on the force, Jae-han is arrested and thrown into a holding cell at the precinct when Hae-young attempts to contact him on the walkie-talkie. Blaming Hae-young, Jae-han refuses to listen until Hae-young reveals that the 9th victim is Kim Won-kyung, a woman whom Jae-han is attracted to. Less than an hour before Won-kyung is to be murdered, Jae-han breaks out of the holding cell and runs to save her.
4
"We Found the Killer"
Kim Won-seok
Kim Eun-hee
January 30, 2016 (2016-01-30)
In 2015, evidence at the scene of the Kyung-soon's murder confirms the murderer was bus driver Lee Chun-goo, but he does not fit the psychological profile of the Gyeonggi Nambu killer. Hae-young realizes the actual culprit of the first 9 murders was Chun-goo's son, Lee Jin-hyung, and the 10th murder was committed by Chun-goo. Soo-hyun gets into a physical confrontation with Jin-hyung in the hospital, but Chun-goo turns himself in and confesses to all 10 murders - without evidence to contest his confession, Jin-hyung will escape prosecution for his murders. In 1989, Jae-han races to save Won-kyung, but is misled by Chun-goo and arrives too late. The next time they speak over the walkie-talkie, an enraged Jae-han demands to know the identity of the murderer so that he can murder them. In 2015, Hae-young realizes that Kyung-soon must have blackmailed Chun-goo for his involvement in the serial murders, and restarted the blackmailing after the removal of the statute of limitations for violent crimes. Hae-young finds the evidence, Won-kyung's glove containing Jin-hyung's DNA, used to blackmail Chun-goo and present the findings to the press as the first solved case of the Seoul cold case squad. As Hae-young is interrogating him in custody, Chun-goo reveals that in 1989, Jae-han confronted him and intent to kill him for Won-kyung's death and realize Jin-hyung was the real culprit. After a brief chase to a rooftop, Jae-han beat Jin-hyung and dropped him from the rooftop, resulting in his paralysis. Chun-goo cover up the incident as he did not want to expose his son's murders. In 2000, Hae-young discovers the corpse of his brother, Park Sun-woo, who had recently been released after being convicted and sentenced to prison for his role in a high school gang rape case, while Jae-han comforts Soo-hyun after her first encounter with a victim's corpse. In 1989, Won-kyung's mother meets with Jae-han, who has resigned from the police force, and reassures him. Later, while Hae-young and Jae-han are talking over the walkie-talkie again, Hae-young explains that while due to Jae-han's efforts, they were able to convict Jin-hyung in 2015, it would not be possible for Jae-han to charge him in 1989 as the technology for DNA matching had not been invented yet. Jae-han mourns Won-kyung while Hae-young resolves to prevent other crimes.
5
"Changing the Past Alters the Present"
Kim Won-seok
Kim Eun-hee
February 5, 2016 (2016-02-05)
In 1995, a rookie police officer named Cha Soo-hyun joins the Special Task Force and becomes the first woman ever assigned to that squad. This causes immediate tensions with the rest of the squad, especially an officer named Lee Jae-han who insists on treating her equally rather than giving her special status due to her gender. The force begin investigating a string of burglaries - Jae-han suspects an ex-convict named Oh Kyung-tae who had a similar MO, but who insists he is innocent. In 2015, Hae-young learns that Jae-han was declared missing in 2001 and discharged from the force, but the case was investigated by Internal Affairs rather than the violent crimes department due to allegations of bribery. This brings Hae-young to the attention of Bum-joo, who insists that Jae-han must never be found. On Bum-joo's orders, Chi-soo begins investigating Hae-young, and discovers security camera footage showing Hae-young finding the discarded police walkie-talkie. Hae-young receives another transmission from Jae-han and is shocked to learn that it is now 1995 for Jae-han, even though only one week has passed for Hae-young since solving the Gyeonggi Nambu murders. Jae-han is desperate to solve the burglary case and demands information from Hae-young; against his better judgement as he fears changing the past could cause people to die who originally lived, Hae-young gives Jae-han some key details of the culprit's psychological profile as the case remains unsolved in 2015. This leads Jae-han to arrest Kyung-tae for the crimes in 1995, resulting in the death of Kyung-tae's young daughter Oh Eun-ji when a bridge collapses. The next day, Hae-young learns that reality has changed again: that case is now considered solved, with Kyung-tae having protested his innocence for 20 years. Kyung-tae is soon released from prison after serving his sentence, and immediately kidnaps a woman named Shin Yeo-jin, uncharacteristically leaving behind key evidence at the scene. Hae-young suspects Kyung-tae's motive for the kidnapping is not for money and learns of Eun-ji's death. The next time they speak, Jae-han tearfully explains that he did everything wrong and it was his fault. Hae-young suspects Kyung-tae plans to murder Yeo-jin.
6
"Catch Him By All Means"
Kim Won-seok
Kim Eun-hee
February 6, 2016 (2016-02-06)
In 1995, following Hae-young's tip a fingerprint is lifted off a mailbox at one of the burglary sites, this along with an eyewitness statement linking Oh Kyung-tae to one of the sites causes an arrest warrant to be put out on him for the burglaries. Jae-han arrests Kyung-tae at his workplace, causing his daughter Oh Eun-ji to have to take a bus home. On the drive back, as they are crossing a bridge it collapses. Both Eun-ji and another passenger, Shin Yeo-jin, are pinned underneath debris and the rescue crew only have the time and resources to save one. Yeo-jin's father, Shin Dong-hoon, insists they save Yeo-jin, leaving Eun-ji to die when the bus explodes. Jae-han later learns from another detective that the fingerprint was falsified and Kyung-tae was not the real perpetrator. In 2015, Dong-hoon receives a call from Yeo-jin revealing she is being held in a refrigerated truck. Hae-young realizes that Yeo-jin is not the intended target but rather it is Dong-hoon, whom Kyung-tae blames for Eun-ji's death. Kyung-tae leads Dong-hoon to another, identical truck that he claims contains Yeo-jin, but on Hae-young's tip Soo-hyun arrives and investigates the truck instead of Dong-hoon. Hae-young realizes too late that Kyung-tae has rigged the truck to explode and is unable to save Soo-hyun, who is caught in the detonation and killed. In 1995 and 2015, Jae-han and Hae-young resolve to continue investigating the now officially solved burglary case and find the real perpetrator. They realize from the ease of the burglaries and the improbability of the culprit to escape the police stakeout at one of the crime scenes that the real perpetrator is Han Se-kyu, the son of one of the four victims, who happens to be the chief prosecutor. In 2015, Hae-young persuades Kyung-tae to help him in catching Se-kyu, while in 1995, Jae-han resolves to find the stolen goods which have yet to be found.
7
"We Must Dig Deeper"
Kim Won-seok
Kim Eun-hee
February 12, 2016 (2016-02-12)
In 1995, Jae-han follows the Han family butler and stops him from destroying Se-kyu's car which contains the stolen items, evidence linking Se-kyu to the string of burglaries. Se-kyu is arrested and charged, and Kyung-tae is exonerated and released from prison. However, Kyung-tae immediately murders Dong-hoon, is convicted of that crime, and later dies in prison, while the Se-kyu case is quickly buried by the chief prosecutor's office and Se-kyu himself is released after only a few months incarcerated. The chief of the Special Task Force reveals to Jae-han that the case is bigger than he thinks and involves an extreme amount of corruption within both the Korean government and the chaebol linked to the construction company related to the bridge collapse accident, and the items Se-kyu stole may inadvertently contain key evidence of collusion. The chief warns Jae-han not to pursue it further as he is fired and replaced with a senior officer named Kim Bum-joo. Jae-han investigates further and finds that the only item reported stolen in the burglaries that was not found in Se-kyu's belongings is a single diamond necklace stolen from a congressman named Jang Young-chul, and focuses on him as the target of his investigation. He finds out that a young woman attempted to sell the missing necklace to a jeweler; security camera footage shows that a floppy disk was found in the necklace's case, which the woman took. Jae-han notices that he has begun to be tailed, likely on Bum-joo's orders. To avoid suspicion and as he has been the only one training the rookie Soo-hyun, he recruits her for his investigation, as she can both move freely and has access to a private room in the precinct. Together they track down the young woman's family, only to find that she has already died. Jae-han discovers that the woman was a girl Se-kyu partied with, and likely stole the necklace from him when he was incarcerated, and resolves to find the disk. In 2015, Hae-young wakes up to find that history has changed again and Soo-hyun has been resurrected, with all of the events involving Yeo-jin's kidnapping having never happened in this reality. Relieved, Hae-young resolves to stop changing the past and refuses to assist with Jae-han's investigation, shredding the case files and disposing of the walkie-talkie. Soo-hyun grows increasingly suspicious of Hae-young after he displays an abnormal level of concern; this suspicion peaks when Chi-soo, who has been tailing Hae-young, retrieves the walkie-talkie from the trash and finds out it was Jae-han's old unit, and informs Soo-hyun. A man meets with the cold case squad and requests them to investigate a matter: that of his fiancee, Shin Da-hye who committed suicide in 1995, but whom the man claims to have seen alive in person recently. Hae-young decides to take the case when he learns that Da-hye was the young woman that Jae-han was searching for 20 years ago. They track down the location where the fiance claimed to have seen her and find a book she left behind; her fingerprint on the book confirms that Da-hye is still alive.
8
"How Are You Alive?"
Kim Won-seok
Kim Eun-hee
February 13, 2016 (2016-02-13)
In 2015, the Seoul cold case squad investigates the 20 year old disappearance of Shin Da-hye. Hae-young interrogates the owner of an entertainment company that employed Da-hye who was an aspiring actress; he learns that the man pimped young girls to events with rich men such as parties that Se-kyu held at his father's cabin. At one of these parties, Se-kyu raped Da-hye, with one of his friends recording the event without his knowledge. This sex tape was then kept by the other boys to potentially blackmail Se-kyu. To remove that threat, Se-kyu stole the copies of the sex tape from the three other families' houses, also taking random valuables to make it look like burglaries. Soo-hyun realizes that after being in hiding for 20 years, Da-hye returned to Korea because her deathly ill mother was in need of an organ transplant, and they track her down at the hospital. Da-hye explains that after Se-kyu retrieved the copies of the sex tape, she stole the necklace as revenge when he refused to destroy or turn over the copies to her. When Se-kyu discovered this, he broke into her apartment at night and murdered a woman in her bed that he believed was her; that victim was actually Da-hye's best friend. When Se-kyu covered up the murder by making it look like Da-hye committed suicide, Da-hye took on the identity of her deceased friend and went into hiding. However, an audio recording of the full murder exists as a tape recorder was left running on the bed that night and was later discovered by Da-hye's sister. That recording, combined with Da-hye's eyewitness testimony under the identity of her friend, is used to formally charge Se-kyu. Se-kyu voluntarily turns himself over to interrogation to contest the recording while ordering Bum-joo to murder Da-hye - however, Soo-hyun foils the attempt while Hae-young reveals that the recording in possession of the cold case squad was not the actual whole recording but rather a copy while the original, longer version proves that Se-kyu was in the apartment that night. When Soo-hyun brings the live Da-hye to the interrogation room, a shocked Se-kyu who recognizes her confesses to the murder. Afterwards, Hae-young questions Da-hye as to the location of the floppy disk, she explains that in 1995 she delivered the disk by mail to Jae-han's precinct. In 1995, Jae-han continues to investigate the missing floppy disk, but it is intercepted by Bum-joo and the incriminating data on the other parties involved is erased. Undaunted, Jae-han vows to Bum-joo that he will continue to investigate any wrongdoing until the whole truth is uncovered. In 2000, it is revealed that it was Chi-soo who shot and killed the wounded Jae-han. In 2015, Hae-young hears once again the distinctive static of the discarded walkie-talkie and is shocked to find it in Chi-soo's desk - he is then confronted by Chi-soo.
9
"Hongwon Dong Case"
Kim Won-seok
Kim Eun-hee
February 19, 2016 (2016-02-19)
In 2015, Chi-soo explains to Hae-young that the walkie-talkie was Jae-han's old unit, which was found with his car when he disappeared in 2001 and kept as evidence until Hae-young found it. Chi-soo threatens Hae-young to cease investigating Jae-han's disappearance but is interrupted by the sudden arrival of other officers; Hae-young retrieves the radio. While performing housework for Soo-hyun's mother, Hae-young discovers Jae-han's notebook that Soo-hyun kept, with a note listing four cases that Hae-young believes were the cases he and Jae-han solved together: the Gyeonggi Nambu murders in 1989, the high profile burglaries of 1995, the Hongwon-dong case of 1997, and the Injoo high school case of 1999, which Hae-young's brother Sun-woo was involved and convicted in, committing suicide shortly after he was released from prison. As the Hongwon-dong case is the next listed, Hae-young attempts to research it only to find no records of any high profile crimes in Hongwon-dong. When next he and Jae-han communicate over the walkie-talkie, it is 1997 for Jae-han and the Hongwon-dong case has yet to happen; Hae-young warns Jae-han. Soo-hyun suggests to the cold case squad that their next investigation be the Hongwon-dong incident, and explains that it was a case wherein two women were found murdered with similar methods of murder and corpse disposal. Upon further questioning Soo-hyun reveals a third set of remains were only recently found that matched the other two bodies, suggesting a serial killer. As the third deceased's time of death dates to 2001, the cold case squad combs the mountain where the third corpse was found for more bodies. Soo-hyun explains that in 1997, there was one additional victim: herself. In 1997, by chance Jae-han stumbles onto a case of two murders that took place in different jurisdictions; he is convinced they are the acts of the same killer. Everything about the two victims were different except that they were both targeted when walking alone at night while wearing headphones. Soo-hyun comes across Jae-han's investigative notes and takes it upon herself to retrace the victims' steps to find any overlap. While doing so she inadvertently copies the profile of the two victims, and chances upon the same convenience store that the second victim visited where the murderer, a clerk named Kim Jin-woo, works. Soo-hyun is targeted and attacked by Jin-woo and wakes up bound in a bathroom. Left unsecured, she escapes and flees out onto the streets and is found by Jae-han. In 2015, many more victims' bodies are found on the mountain.
10
"Someone Has to Stop the Bad Guys"
Kim Won-seok
Kim Eun-hee
February 20, 2016 (2016-02-20)
In 1997, the traumatized Soo-hyun considers giving up on being a cop, but on Hae-young's advice Jae-han reassures her. In 2015, a total of eight additional bodies are found on the mountain. In addition to the first corpse found that triggered the search and the two victims that were found in the streets, the Hongwon-dong killer is believed to be responsible for 11 murders. On Bum-joo's suggestion, the Hongwon-dong case is assigned to the Seoul cold case squad. Bum-joo warns Chi-soo that the penalty for failure will be severe. The respective teams in 1995 and 2015 both attempt to find Jin-woo's house via details recounted from Soo-hyun's capture; both fail. Hae-young and Jae-han share details of their respective investigations across time: Jae-han is shocked to hear that Soo-hyun becomes the leader of the cold case squad while Hae-young does not have the heart to tell Jae-han that he is missing and presumed dead in the present. On Hae-young's suggestion, the cold case squad focuses their efforts on the 11th body, the only victim they failed to identify, who was murdered in 2014 and who Hae-young believes Jin-woo had an emotional connection to. In flashbacks, it is revealed that Jin-woo was abused by his mother as a child. The resultant neuroses caused each of the various habits that signify his murders. The 11th victim was a woman, later identified by DNA as Yoo Seung-yeon, who was infatuated with Jin-woo and over the years they developed a relationship. Using forensic details of Seung-yeon's bones, Hae-young locates her former workplace and finds a journal, getting key details that allow him to deduce that the victims all shopped at the same convenience store. Hae-young visits each store in the area questioning clerks until he finds the one Jin-woo worked at. Meanwhile Soo-hyun retraces her own steps and arrives at Jin-woo's home. Finding the door unlocked, she enters.
11
"The One Last Case"
Kim Won-seok
Kim Eun-hee
February 26, 2016 (2016-02-26)
In 2015, the police ransack Jin-woo's home, finding a wealth of evidence linking him to each of the victims and even the bones of his mother kept in a closet, but Jin-woo himself has gone missing. Hae-young realizes that after Seung-yeon's murder, Jin-woo is planning to commit suicide at the same location where he buried the bodies, no longer able to murder after killing someone he had genuine affection for in Seung-yeon. Soo-hyun arrives just in time as Jin-woo hangs himself and prevents his death. The next time they speak, Jae-han learns that they have solved the case in 2015 and demands to know the identity of the perpetrator, but Hae-young refuses to answer in order to avoid changing history and causing more unexpected deaths. However, when Hae-young looks at his note of solved cases, the line for the Hongwon-dong case disappears before his eyes: history has changed again. He discovers that Jin-woo has vanished from custody and is instead in a mental institution after having been arrested by Jae-han who independently solved the case in 1998, preventing the nine additional murders that started in 2001 - each of the nine women are now alive and well. The next time the walkie-talkie is active again, it is now 1999 for Jae-han, with only one case remaining that was listed in the notebook: the Injoo high school case involving Hae-young's brother Sun-woo. Hae-young pleads with Jae-han to find the truth of the case. In 1999, then 9-year old Hae-young is living in Injoo with his mother and Sun-woo. At their high school, a female student named Kang Hye-seung attempts suicide after accusing 18 male students of gang rape. The allegation takes the form of an unusual poem that soon spreads, causing a citywide scandal. As Injoo is undermanned for such an extensive investigation, reinforcements from the special task force are requested - Jae-han interjects himself into this squad, led by Bum-joo. At Injoo, Jae-han partners with a local, a young detective named Ahn Chi-soo. After receiving a photograph from a student, Jae-han begins to suspect that the poem contained a code. In 2015, Bum-joo threatens Chi-soo, only for Chi-soo to tender his resignation. Chi-soo then calls Hae-young and warns him not to continue his investigation of the Injoo case, only for Hae-young to refuse. Chi-soo requests a meeting with Hae-young at the Injoo hospital, promising to come clean and claiming he orchestrated the entire affair, but when Hae-young arrives he finds Chi-soo seriously wounded.
12
"The Case Was Manipulated"
Kim Won-seok
Kim Eun-hee
February 27, 2016 (2016-02-27)
In 1999, Jae-han figures out the code from the poem and the photograph and shifts his focus to the Injoo high school student council, while Bum-joo works with the local chief of police to immediately evacuate all seven of those students from the city. Jae-han suspects one of the seven is the actual author of the poem with the rape allegation acting as whistleblower; this student, Lee Dong-jin, is to be spirited out of the city by Chi-soo, but Jae-han intercepts them and brings Dong-jin into custody. Dong-jin begins to recount the incident that began with Sun-woo privately tutoring Hye-seung at a remote house owned by Dong-jin's family, but the interrogation is interrupted when Dong-jin's father arrives and takes him away. The next time Jae-han is able to question any of the council students, they have already had time to prepare fabricated statements - each gives an identical testimony blaming Park Sun-woo for instigating the gang rape, even Dong-jin. Next Sun-woo himself is brought in for interrogation, and reveals that he was the one who sent the photograph to Jae-han. Investigating further, Jae-han discovers a discrepancy in the witness testimonies and after pressing one of the locals, learns that all of the witness and investigator statements were coached. In a rage Jae-han then confronts Kim Jung-jae, one of his fellow officers from Seoul and his best friend, who confesses that he was paid to cooperate with the frame, and as he had recently learned from his wife that they were about to lose their house, could not refuse. The final piece of evidence is when Hye-seung herself gives a statement naming Sun-woo. In 2015, a dying Chi-soo confesses to Hae-young that he was the one who killed Jae-han, and begs Hae-young to tell Jae-han that he had no choice. Chi-soo gives a cryptic statement claiming "it all started in Injoo", and perishes from his wound. Under interrogation, Hae-young admits that he was called there by Chi-soo to discuss the Injoo high school case which the section chief claimed was fixed. Bum-joo orders an immediate investigation of the homicide enlisting all officers, but excludes the cold case squad as Hae-young is considered the prime suspect. A witness statement providing motive for Hae-young is then given by a man named Kim Sung-bum, who was the key witness in Jae-han's bribery allegation and that Hae-young suspected of working with Chi-soo. Under pressure, Hae-young reveals to Soo-hyun that Chi-soo killed Jae-han and framed him for the bribery allegation in 2001. Later, Hae-young explains to Soo-hyun that in 1999, officers investigating the Injoo high school case arrived one day and arrested Sun-woo, later convicting him of a crime. Hae-young's father believed these allegations while their mother did not, causing a divorce. The father took the then 9-year old Hae-young with him to Seoul, the next time Hae-young saw his mother again she had committed suicide, while Sun-woo also committed suicide shortly after being released from prison. Some time later, a teenage Hae-young learns from a rumor that the key evidence leading to Sun-woo's conviction was eyewitness testimony from a student - he tracks the student down who reluctantly admits he was instructed to give the fabricated testimony by the police, this instills in Hae-young a deep-seated hatred of law enforcement. Soo-hyun tracks down Jung-jae, who had resigned from the force after returning to Seoul from the Injoo case, but even after revealing Chi-soo's death and deathbed confession of Jae-han's slaying, Jung-jae refuses to talk. When Hae-young next returns to the precinct, by chance he witnesses Sung-bum leaving and realizes he saw Sung-bum's car outside the Injoo hospital. Soo-hyun and Hae-young find and investigate a house listed under Sung-bum's mother's name that Hae-young believes may have been used to store evidence, and find nothing. However, right as they prepare to leave, Hae-young recalls something Chi-soo said before he died and digs under the stairs in front of the house, discovering the skeletal remains of Lee Jae-han.
13
"The Real Assailant"
Kim Won-seok
Kim Eun-hee
March 4, 2016 (2016-03-04)
In 2001, after Lee Jae-han goes missing, he is framed for bribery by other officers. Soo-hyun is the only one who disbelieves this and resolves to find him, taking possession of his belongings including the notebook with his detailed case notes. In 1999, the Special Task Force squad returns to Seoul, and Jae-han prepares to submit his resignation due to his failure to prevent the framing of Park Sun-woo, but is convinced to stay by Soo-hyun. After remembering Hae-young's pleas over the walkie-talkie, Jae-han realizes the Park Hae-young he is talking to through time is the younger brother of the convicted Sun-woo. Tracking down the 9-year old Hae-young in Seoul, Jae-han discovers him neglected by his father and begging for food. Jae-han begins to watch over Hae-young, paying off a local restaurateur to feed the child. Hae-young grows up to become a troubled teenager and continues to eat at the same eatery. Remembering that the student witness who framed his brother claimed Sun-woo was chosen because he was poor and weak, Hae-young resolves to become strong, excelling in academics and eventually joining the police academy as it is the only high-end educational institution willing to overlook his history of delinquency. In 2015, the remains of Jae-han are brought in and positively identified, and a funeral is held for him. Hae-young finds the business card of the restaurant he used to eat at in Jae-han's belongings and questions the owner, discovering the truth of his secret benefactor. In 1999 and 2015, Hae-young and Jae-han talk across time on the walkie-talkie. Having changed his mind, Hae-young attempts to alter history by convincing Jae-han to give up on the Injoo case in order to prevent his death in 2001, but Jae-han refuses, promising that he will see the case to the end no matter the risk to himself. In 2015, while the police are investigating Hae-young for Chi-soo's murder with Kim Sung-bum having mysteriously vanished immediately after news of Jae-han's remains being found were leaked, Soo-hyun decides to have the cold case squad investigate the officially solved 1999 Injoo high school case, starting by searching for the surviving victim, Kang Hye-seung. Hae-young and Soo-hyun find the adult Hye-seung, who explains that the young Hye-seung was abused by her alcoholic father and Sun-woo was her only friend. When the rape allegation poem was released on the Internet by Lee Dong-jin, Hye-seung attempted to commit suicide by jumping off the high school's roof, but was stopped by Sun-woo. Later, Hye-seung was forced by her father to give the false testimony prepared by Bum-joo blaming Sun-woo for instigating the gang rape - the real culprit was a member of the student council.
14
"Not Now, But Maybe in the Past"
Kim Won-seok
Kim Eun-hee
March 5, 2016 (2016-03-05)
In 2015, Kang Hye-seung explains that the real perpetrator was a boy named Jang Tae-jin, the son of the president of Injoo Cement, a construction corporation that held power and influence in the town, and the nephew of Jang Young-chul, an influential congressman. When Hae-young offhandedly mentions that Sun-woo had committed suicide, Hye-seung is in disbelief, revealing that she had visited Sun-woo in prison shortly after he was sentenced, and the elder Park brother had consoled her and claimed he was going to start a new life once he had been released. As the statute of limitations on rape has long since expired and Hye-seung is unwilling to testify anyways as she now has a normal life and family, the cold case squad cannot touch Tae-jin for this crime, but Hae-young realizes it is still possible to change the past and prevent the deaths of both Sun-woo and Jae-han. Suspicious of Hae-young's cryptic statements, Soo-hyun goes to meet with him at his home that night. In 2000, with the Injoo high school case closed, Jae-han has now shifted his focus to investigating Bum-joo himself, and threatens the station chief in a heated confrontation. Bum-joo then returns the favor by threatening Jae-han's father, but Jae-han refuses to stop investigating. Later, while on a stakeout with Soo-hyun, Jae-han is asleep when Hae-young hails him on the walkie-talkie. Across time in 2000 and 2015, the younger and older versions of Soo-hyun simultaneously witness Hae-young attempting to reach Jae-han on the radio. Remembering what her younger self saw that night, the 2015 Soo-hyun finds Jae-han's walkie-talkie in Hae-young's apartment. In 2000, a few months after the resolution of the case, Sun-woo and the other students implicated are released from incarceration. Sun-woo finds and meets with Lee Dong-jin and forgives him, only requesting Hye-seung's red scarf. Out of guilt, Dong-jin decides to leave the country and study abroad, while instructing a fellow student to bring the red scarf to Sun-woo along with his apologies. While investigating Jae-han's broken walkie-talkie, Soo-hyun chances upon a detective who was Jae-han's partner before he joined the Special Task Force, who believes that Jae-han holds onto the walkie-talkie as a memento of Kim Won-kyung, his first love who was murdered by the Gyeonggi Nambu killer. In her jealousy, Soo-hyun sustains a minor ankle injury. Later, Jae-han receives a call from Sun-woo urgently requesting a meeting and claiming he has new evidence. Instead of going to meet with Sun-woo immediately, out of concern Jae-han accompanies Soo-hyun on a burglary bust, where he is stabbed and seriously wounded by the suspect - a distraught Soo-hyun later confesses her love for Jae-han in the ambulance. In 2015, Hae-young discovers Chi-soo had requested the case files of the Sun-woo suicide investigation before he died. He retraces Chi-soo's movements and discovers a blood sample in the Injoo hospital of Sun-woo's, proving that he had been sedated when he died. Soo-hyun confronts Hae-young with the walkie-talkie demanding to know the truth, and Hae-young comes clean, revealing how he had been in contact with Jae-han since the beginning of the Kim Yoon-jung case, using the communications to solve the cases, change the past, and even prevent the death of Soo-hyun that had occurred in a separate reality's 2015 in the Shin Yeo-jin kidnapping. While Soo-hyun is in disbelief, the walkie-talkie becomes active again, and Hae-young begs Jae-han to save Sun-woo, giving him the exact date of his death. In 2000, the wounded Jae-han leaves the hospital and races to save Sun-woo.
15
"Is It Really You?"
Kim Won-seok
Kim Eun-hee
March 11, 2016 (2016-03-11)
In 2000, while the wounded Jae-han drives to Injoo to meet with Sun-woo, Bum-joo arrives at Sun-woo's house, having received a tip from the Injoo police precinct. Sun-woo confesses to Bum-joo that the real perpetrator was Jang Tae-jin and reveals Hye-seung's red scarf. When Sun-woo explains that his motivation for clearing his name is to mend the rift between his mother and father, Bum-joo, who is protecting Tae-jin due to an imminent parliamentary meeting involving his uncle Jang Young-chul, decides to murder Sun-woo, lacing his drink with sedatives. Jae-han arrives too late and Sun-woo is found by Hae-young, with his murder being declared a suicide. Searching the house, Jae-han is unable to find the scarf, and learns from the officer at the precinct that Bum-joo had been tipped off to Sun-woo. Jae-han then violently confronts Bum-joo in his office. Defeated, Jae-han requests a transfer to a different precinct and gives a farewell to Soo-hyun. In 2015, Hae-young is arrested by the police for the murder of Ahn Chi-soo. Hae-young entrusts the walkie-talkie to Soo-hyun while he is taken into custody. The murder weapon, a knife, is found at Injoo hospital with Chi-soo's blood and Hae-young's fingerprints, while multiple eyewitnesses who had seen Hae-young after he discovered Chi-soo's body also implicate him for the crime. The next time the walkie-talkie becomes active again, Jae-han is eager to apologize to Hae-young for his failure, but it is instead the older Soo-hyun on the other end in 2015. Tearful, Soo-hyun attempts to prevent Jae-han's killing by telling him the exact date of his death and warning him to stay away from the location where it happened. In 2015, Soo-hyun meets with Hae-young in detention and demands to know if the past can be changed. She explains that she told Jae-han the date of his death, but Hae-young reveals that in the very first transmission he had ever received from Jae-han, it was on the day of his death and Jae-han had said that he had been warned not to go to that place - Jae-han knew of the danger and went anyways, discovering the body of Seo Hyung-joon had been a total coincidence. The cold case squad realize that Kim Sung-bum is also on the run now, due to Bum-joo needing someone to take the fall for the murder of Jae-han now that his remains had been found. Hae-young realizes it was Sung-bum who had attempted to contact him several times previously, and the squad retrieves his phone from evidence, where there is a message from Sung-bum requesting a meeting with Hae-young. Knowing that Sung-bum, an experienced criminal, would disappear if it is not Hae-young who arrives at the meeting location, Soo-hyun helps Hae-young to escape from police custody. They meet with Sung-bum, who reveals the truth of Jae-han's death: after transferring in 2000, Jae-han continued to investigate the Sun-woo suicide case, and somehow obtained forensic analysis implicating Bum-joo. By chance, the Kim Yoon-jung kidnapping case occurs, and Special Task Force reinforcements led by Bum-joo arrive and take over. While Jae-han is investigating that case, Bum-joo discovers the forensic evidence. Jae-han is then captured and tortured for information by Bum-joo, Sung-bum, and Chi-soo, but attempts to escape through a forest. Dying of a fatal stab wound, Jae-han makes his final radio transmission to Hae-young, telling him to convince his 1989 self and never give up as the past can be changed, before Chi-soo shoots and kills him. In 2015, Sung-bum is then killed by an agent sent by Bum-joo. The hitman then fires a shot at Soo-hyun; Hae-young leaps into the path of the bullet.
16
"If You Don't Give Up"
Kim Won-seok
Kim Eun-hee
March 12, 2016 (2016-03-12)
In 2015, while Hae-young is dying from the bullet, he and Soo-hyun desperately wait for the walkie-talkie to become active, but it does not. Hae-young later dies in the hospital. In 2000, days before Lee Jae-han dies, Kim Bum-joo discovers that Jae-han somehow obtained Kang Hye-seung's red scarf implicating Jang Tae-jin in the gang rape, and orders Chi Ahn-soo to follow him and retrieve it. Cha Soo-hyun transfers to the precinct and wants to speak with Jae-han, but he promises his investigation will be over soon and asks her to wait until then. In the original reality, Soo-hyun waits for over 15 years before Jae-han's remains are found in Sung-bum's country home. At the psychiatric hospital where Seo Hyung-joon's body was dumped, Jae-han delivers the very first radio transmission that Park Hae-young ever received, telling him the location of Hyung-joon's corpse, before he is knocked unconscious by Chi-soo. Jae-han later wakes up in an abandoned warehouse with Chi-soo, Bum-joo, and Sung-bum. It is revealed that after Bum-joo had murdered Park Sun-woo and retrieved the scarf, he had discarded it in the trash at a rest stop. Jae-han deduced this and managed to find the scarf at a landfill. Knowing that the police in Korea could not be trusted, he sent it to the United States for forensic analysis, and was later mailed the results, obtaining key evidence not only in the Injoo high school case, but also Bum-joo's blood linking him to Sun-woo's death. Bum-joo interrogates Jae-han as to who else knows about the scarf, but Jae-han breaks free of his bindings and flees into the forest. Right before Chi-soo fires the bullet that originally kills Jae-han, other officers appear on the scene and rescue him - this time, Jae-han had notified others where he was going. Jae-han and Soo-hyun later go on their first date to celebrate. In 2015, Hae-young suddenly wakes up after dying in the hospital, to find himself in his own apartment, but somewhat unfamiliar. He discovers nearly his entire life has been changed - in this reality, Jae-han had personally delivered the news to Hae-young's parents that Sun-woo had been posthumously exonerated, so his parents had never divorced. Hae-young tries to track down the cold case squad only to find that it no longer exists and the other two members, as well as the rest of the police, do not recognize him. Furthermore, in this new reality, Lee Jae-han is still missing and presumed dead, having disappeared at a later date in 2000: after tracking down Bum-joo, believing he had another copy of the floppy disk inadvertently stolen by Han Se-kyu and then again by Shin Da-hye implicating Jang Young-chul and many others in a corruption scheme, Jae-han and Bum-joo had been attacked. Bum-joo's corpse was later found at the scene, but not Jae-han's, who had escaped and then been framed for the murder. Remembering the notebook Jae-han had kept where he detailed the case notes for the four cases he and Hae-young had solved, Hae-young retrieves the notebook from evidence and finds an address written inside; the address is of his parents' house, who had received a letter from Jae-han containing the floppy disk and imploring Hae-young to continue the investigation. While searching the location where the envelope was mailed from, Hae-young chances upon Soo-hyun, who also remembers the original reality. Soo-hyun explains that after Jae-han's disappearance in 2000, she received a call that she believed was from him and tracked it down to the same location then. She had then searched for him for 15 years, never finding him alive or dead. However, a few days prior she received a strange text warning her to stay away from a certain treatment facility.They theorise either Jae-han is indirectly signalling them to come in there or someone from future is in contact with him. Holding out hope, Hae-young and Soo-hyun drive to that location, where it is revealed that Jae-han is still alive and is about to answer the active walkie-talkie thus confirming the latter's future theory to be true.
Upon its premiere, the series attracted attention for weaving actual cases into its plot and attained high ratings.[11][12] With its finale rating of 12.54%, it is one of the highest rated Korean dramas in cable television history.[13][14] It received praise for its solid acting, tightly-constructed plot and detailed and sophisticated direction; and enjoyed success internationally in China and Japan.[15][16][17]
The drama went on to win several awards from different award-giving bodies, including Best Drama, Best Screenplay for Kim Eun-hee, and Best Actress for Kim Hye-soo at the 52nd Baeksang Arts Awards, as well as another Best Actress award for Kim and the Daesang (Grand Prize for Television) for Cho Jin-woong at the tvN10 Awards. Cho also won the Daesang at the 1st Asia Artist Awards for his performance.
In this table, the blue numbers represent the lowest ratings and the red numbers represent the highest ratings.
This drama airs on a cable channel/pay TV which normally has a relatively smaller audience compared to free-to-air TV/public broadcasters (KBS, SBS, MBC and EBS).
^Jang, Jin-ri (March 14, 2024). '시그널' 시즌2 나온다...김은희 작가 "'범죄도시' 제작사와 준비 중" ['Signal' Season 2 coming out... Writer Kim Eun-hee, "We are preparing with the production company of 'Crime City'"] (in Korean). SPOTV News. Retrieved March 14, 2024 – via Naver.
^Lee, Mina (August 20, 2015). "이제훈, tvN 드라마 '시그널' 출연". Oh My Star News (in Korean). Retrieved August 27, 2019.
