Kim Hyeong-min Kim Yun-seok is a widowed narcotics officer who meets the informant named Kang Ju Ji-hoon at a restaurant, and what begins as a tense conversation soon lands Kang in the homicide division for murdering his girlfriend. He confesses to that crime and is sent behind bars, leaving Kim to navigate a fragile sense of justice on his own.
A few months into his probation, Kang reaches out from prison with a shocking claim: he has murdered six more people. He refuses to talk to the detectives who he believes manipulated the case to put him away. Kim accepts the daunting bargain of trading information about the six bodies for inside details from Kang, hoping to uncover real evidence that could prove his innocence or reveal a deeper corruption. As Kim follows the threads, he uncovers material proof that contradicts the original investigation, suggesting the homicide detectives fabricated key elements of Kang’s case. The revelation leads to charges against the detectives and a reduction in Kang’s sentence, while Kang promises to disclose information about the remaining victims.
Among the six alleged victims, the first target Kim investigates is Oh Ji-hee Kwon So-hyun, a former swimmer who is forced to work at a nightclub to support her grandmother in the village. Kang asserts that he killed Oh Ji-hee one night after driving her away from the city, where he worked as a cab driver. Yet as Kim digs deeper, he encounters a chorus of warnings from people around him that Kang cannot be trusted. Still, he presses on. Part of Oh Ji-hee’s remains surfaces thanks to Kang’s tip, but when Kang is pressed in an interview, he claims that Kim used coercion and bribes to elicit false statements. Even more troubling, DNA testing reveals the remains do not belong to Oh Ji-hee. With this uncertain state of evidence, the prosecutor cannot indict Kang.
Feeling frustrated and betrayed, Kim seeks guidance from his former mentor, Song Kyeong-soo Ju Jin-mo. Song counsels Kim to step back, arguing that Kang is trying to project innocence in other crimes to overturn his current sentence. Kim also learns from Kang’s older sister the darker truth that Kang killed their father when he was a boy and that she helped cover up the murder. This revelation helps explain Kang’s trajectory into serial killing, but it also seals the reality that much of this history lies beyond the reach of the statute of limitations.
With a new partner, Detective Jo Jin Sun-kyu, Kim resumes the hunt and turns his focus to a second victim, Hwang. Kang claims he killed Hwang by pushing her down a flight of stairs. The two scour old case files and uncover one that matches Hwang’s murder, bringing the matter to trial. However, the case hinges on circumstantial evidence, and Kang escapes conviction. The fallout is swift: Kim is demoted and Jo is transferred to the narcotics division, leaving Kim to wrestle with the cost of chasing truth in a system that seems to bend under pressure.
As Kim continues to connect the dots, a crucial clue emerges from a crime-scene photo: an IUD birth control implant found among unidentified remains. This detail prompts Kim to compile a list of women who had IUD implants around the time of the murders. Among them is Park Mi-yeong Bae Hae-seon, Kang’s girlfriend at the time, who had moved to the city with her young son. Park begins to realize that breaking away from Kang could threaten her safety, and she tries to leave him, an act that precipitates her murder. Kim tracks Park’s teenage son and brings him to testify, exposing Kang’s pattern of coercion and violence in court. In the end, Kang Tae-oh’s reign of fear is brought to a close as he is sentenced to life imprisonment, and the case grounds itself in a more complete, if painful, picture of the crimes and their consequences.
Throughout this investigation, Kim’s resolve is tested by distrust, old wounds, and the limits of the law. Yet he persists, driven by a stubborn commitment to uncover the truth behind Kang’s alleged six additional murders and the ways in which the system failed to see the horror right in front of it. The film leaves a quiet, grave impression on the idea of accountability, the cost of seeking justice, and the fragile line between truth and manipulation.
