One snowy night, a school-bus driver named Carlos meets a pregnant woman named Michelle and offers to fix her flat tire. After knocking her unconscious, Carlos drops Michelle off at her house and while doing so, Michelle's ring falls off. Carlos ignores this and scatters the body parts in a local stream. When a boy discovers one of Michelle's ears, the police arrive en masse to conduct a search led by Section Chief Steve and Squad Chief Dave, Michelle's devastated father. The victim's fiancé, Andy Shaw, a CSIS officer, is also present and vows revenge against the killer.
Andy learns about the four suspects from Squad Chief Dave and proceeds to privately harangue and interrogate two of them. Searching the home of the third suspect, Carlos, Andy finds Michelle's engagement ring, proving that Carlos was the culprit. A short time later, Carlos brings home a female student and assaults her. Andy knocks her unconscious. Rather than kill Carlos and be done with him, Andy decides to insert a GPS tracker down his throat, allowing him to see Carlos' location in real time and listen in on his conversations.
Waking up injured, Carlos walks into the street and is offered a ride by a taxi already carrying one passenger. Upon entering, and correctly guessing that the driver and passenger are in fact two outlaws intent on robbing and murdering him, one being Andy's fourth suspect, he attacks and kills the first. kills them both. Later, he finds the real taxi-driver's body in the trunk. Carlos dumps all three bodies outside, and drives to a small town where he sexually assaults a nurse. Andy arrives to subdue him and cut his ligaments before releasing her once again.
Carlos visits the home of his friend Butch, a murderer and cannibal. After explaining his situation to Butch, the latter remarks that whoever is behind him must be a relative of one of his victims. Carlos guesses Andy's identity after remembering Michelle's engagement ring, which Andy had previously been wearing before attacking him. Andy arrives and incapacitates both killers, along with Butch's girlfriend Tabitha. The next day, Butch and Andy, still unconscious, are arrested by the police and sent to the hospital.
Andy's trusted subordinates arrange for Andy and Carlos to escape the police and be treated for their wounds at an isolated facility. Barely conscious, Carlos overhears Andy and the subordinate talking about the transmitter. Andy releases Carlos again, but the latter overpowers Andy, slitting the throat of a pharmacist while stealing laxatives, which he uses to remove the transmitter, then turns it on a driver at a truck stop. whom he viciously beats. Andy enters Butch's hospital room to question him, and learns too late that Carlos is going after squad chief Dave and his other daughter, Samantha. In a fit of rage, Andy breaks Butch's jaw.
Carlos arrives at Dave's house, and brutally assaults him, then kills Samantha. Shortly afterwards, Carlos attempts to escape Andy's retribution by surrendering to the police. However, Andy drives up and kidnaps Carlos in front of the police. Taking him to an earlier warehouse, Andy tortures him, puts him under an improvised guillotine, and leaves him holding a rope between his teeth to keep the blade from falling.
Although he makes fun of Andy, Carlos panics when he learns that his son and elderly parents, whom he abandoned some time ago, have arrived and are trying to visit him. As his family opens the door despite their stifled protests, it triggers another mechanism set up by Andy which drops the blade and brutally cuts Carlos in front of his family. With Carlos finally dead, Andie, who was listening in via transmitter at a distance, has an emotional breakdown as she realizes that his "revenge" solved nothing, killed innocent people, And ultimately will never let him feel better.
