As the school-bus driver, Jang Kyung-chul, halts to help a stranded Jang Joo-yun, her tragic fate is already sealed by his malevolent intentions. In a horrifying turn of events, Kyung-chul brutally attacks and dismembers Joo-yun, carelessly scattering her remains into a nearby stream. The horrifying discovery of these body parts sets off a massive search operation, spearheaded by Squad Chief Jang, who also happens to be Joo-yun's father. Meanwhile, her fiancé, Kim Soo-hyun, is determined to seek revenge on the monster behind this heinous act.
In the throes of his vengeance, Soo-hyun interrogates two suspects and uncovers the disturbing revelation that Kyung-chul is among the four potential attackers. A search of Kyung-chul's home yields Joo-yun's ring, a grim token that fuels Soo-hyun's relentless quest to find and punish the killer.
Kyung-chul's depravity takes another turn when he abducts and assaults a schoolgirl, leading Soo-hyun to take extreme measures. He subdues Kyung-chul and forces him to swallow a tracker device, granting him the ability to monitor the killer's movements and overhear his twisted conversations.
As Kyung-chul roams the city, his behavior spirals into chaos and violence. He brutally slaughters two taxi passengers and, in need of medical help, crosses paths with a nurse who becomes his next victim. Just when it seems that Kyung-chul's savage reign might continue unchecked, Soo-hyun intervenes again, inflicting harsh retribution by slicing through Kyung-chul's Achilles tendon.
Kyung-chul's ensuing visit to his friend Tae-joo, another despicable murderer and cannibal, sets off a captivating sequence of events that reveals Soo-hyun's identity. Realizing who is tormenting him, Kyung-chul becomes equally fixated on revenge, intensifying their deadly game.
This cat-and-mouse chase escalates as both men receive treatment for their wounds while staying one step ahead of the law. Kyung-chul’s cunning maneuver to ditch the tracker and frame another driver is discovered by Soo-hyun, heightening the stakes in their deadly struggle.
As tensions rise, Soo-hyun's fury erupts in a hospital confrontation with Tae-joo, who inadvertently divulges Kyung-chul's sinister plan to target Squad Chief Jang and his other daughter, Jang Se-yun. Driven by rage, Soo-hyun brutalizes Tae-joo, leaving him a battered shadow of his former self.
The dramatic intensity reaches a chilling climax when Kyung-chul unleashes a frenzy of violence against Jang, leading to a shocking slaughter that leaves destruction in his wake. Attempting to escape punishment by turning himself in to the authorities, Kyung-chul is thwarted when Soo-hyun seizes the chance for vengeance, snatching him away right beneath the police’s noses.
In a macabre twist, the scene shifts to Kyung-chul's hideout, where Soo-hyun unleashes a storm of torment upon him, binding him with a makeshift guillotine and forcing him to grasp a rope between his teeth to stave off an impending fate. As he faces the horrific consequences of his actions, Kyung-chul initially mocks Soo-hyun's cruelty but quickly succumbs to panic when he learns that his estranged son and elderly parents have come to pay their respects.
This family reunion inadvertently triggers a mechanism that sends the blade of the guillotine into a deadly descent, brutally beheading Kyung-chul before the shocked eyes of his family. Overcome with tears, Soo-hyun stands amidst the chaos, her sorrow mingled with a profound sense of grim satisfaction as she walks away from the aftermath of this gruesome ordeal.
