After a stranger photographs the damage to a man’s car and then takes a life to submit the evidence for an insurance claim, a chilling pattern begins to emerge. A seasoned detective, Jung Tae-suk, walks the crime scene and suspects a serial killer may be at work, yet his commanding officer remains skeptical. The killer’s method is cold, calculated, and seemingly random, leaving investigators with more questions than answers while a city anxious for answers watches.
On the same fateful route home, crime boss Jang Dong-soo is ambushed by the same killer. A brutal confrontation leaves both men battered, and the killer manages to escape as Dong-soo collapses. Dong-soo is rushed to the hospital, where his crowd of loyal henchmen misinterpret the attack as the result of a rival gang, prompting a counterstrike. Meanwhile Tae-suk, still convinced there is a unified thread to the killings, pushes his case forward, but Dong-soo refuses to cooperate at first. He wants the killer found by his own people and simply insists that the killer belong to the side that captures him first, a demand born of revenge and a ruthless sense of pride.
Deciding to pool their resources, the two men strike a wary alliance. Dong-soo agrees to supply manpower and cover expenses, but with a crucial caveat: the killer will belong to whoever finds him first. Tae-suk, driven by a desire to solve five linked murders and earn a promotion, agrees to work with Dong-soo, even as he remains mindful of the mobster’s volatile nature. The collaboration intensifies when Dong-soo orders his right-hand man to kill his rival Heo Sang-do using the killer’s knife, a move that shocks Tae-suk and leaves the case in jeopardy as it crosses line after line in the law and in principle. The tension between desire for justice and thirst for vengeance soon erupts into public violence, forcing the major crimes squad to take charge of the investigation.
Funerals, whispers, and new leads propel the case forward. At Sang-do’s funeral, the killer appears and reveals to Sang-do’s second-in-command that Sang-do was killed with the killer’s knife, though not by Sang-do’s own hand. As Tae-suk and Dong-soo scour the killer’s car for evidence, they are ambushed by Sang-do’s henchmen, and the ensuing clash claims the life of Sang-do’s loyal ally. The shock of bloodshed fuels the investigation, and Tae-suk doubles down on his theory that the killer is a missing person, a discovery that hinges on forensics and careful listening to witness testimony. Dong-soo shares what he knows only with Tae-suk, and the two men begin to close in on the killer’s trail.
When Tae-suk identifies the killer as a missing person, he brings this crucial insight to Dong-soo and the two men once again join forces. A high school girl’s disappearance adds another layer of urgency to the manhunt: Dong-soo offers shelter and protection to those around him, but a girl who bears his umbrella is found murdered, her crime scene bearing the unmistakable mark of the killer. The umbrella, discovered in Dong-soo’s possession, becomes a powerful clue that drives them toward a final confrontation. The chase moves into high gear as the killer vanishes and then resurfaces in a car, and a desperate pursuit ensues. The killer manages to kill Dong-soo’s trusted ally Oh-sung, but is ultimately captured—though not before a brutal moment of defiance from Dong-soo, who tries to finish the killer off in his own brutal way.
Tae-suk intervenes when the assault threatens to spiral out of control, slamming his vehicle into the hideout to prevent an extralegal ending. The race to secure a confession comes down to a single question: can the killer be held for a crime that has snared multiple victims without clear, undeniable evidence? Tae-suk confronts Dong-soo’s dubious choices and demands his partner provide testimony that might seal the killer’s fate. Dong-soo does testify, offering decisive statements that anchor the case in truth, while also leveraging information that might mislead the court to ensure the killer bears the consequence of his actions.
At the trial, the jury delivers its verdict: Kang Kyung-ho is sentenced to death based on the weight of the evidence and the drama surrounding the case, but Dong-soo’s own illegal activities come to light, resulting in his arrest alongside Kyung-ho. Tae-suk’s steadfast pursuit pays off as he is finally promoted, while Dong-soo faces prison as promised, the condition he set in exchange for his testimony bearing fruit. In a final, chilling moment within the prison walls, Dong-soo spots Kyung-ho and steps inside with a rope and a smile, a stark reminder that in his world, justice and vengeance remain two sides of the same entrenched coin.
