Max is a cab driver in Los Angeles. One night he picks up Annie, a beautiful DA. The two have very friendly chat where Annie talks about her nervousness over her upcoming trial appearance and Max discusses his dream business, a limo company. At the end of the ride Annie gives Max her card. Annie leaves the cab and goes inside her building to work on her important case.
A man approaches the cab, and Max almost doesn't notice him, but he gets the man in anyway. The man introduces himself as Vincent. He's very friendly and offers Max $600 to drive him around for the entire night. Max reluctantly agrees. As the two chat, Vincent says that he hates Los Angeles because it is impersonal. He recalls a news story about a man who died on the subway but remained on the train for hours without anyone noticing. Max tells Vincent about his dream of opening a limo company, describing his job as a cab driver as temporary. Vincent asks how long he has been doing it, and Max confesses that his "temporary" job has lasted 12 years.
Vincent has Max drive him to an apartment building. Vincent goes upstairs as Max eats a sandwich. Suddenly, a dead body falls on the roof and windshield of Max's cab, breaking the glass, denting the roof and breaking the light dome on top. Vincent comes downstairs and reveals that he shot the man. He forces Max at gunpoint to help him hide the body in the cab's trunk. They wash the blood off the car an repair the light dome. Max begs Vincent to let him go, but Vincent insists that he go with him. They are later pulled over by the LAPD, who notice the damage to Max's cab. Max is able to stall them for a few minutes by saying he hit a deer; the police are called away to handle another incident. Not long after, Max receives a call from his boss, who had received a call from the police informing him of the damage. Vincent instructs Max to tell his boss off and poses as an attorney, telling Max's boss that insurance will pay for the damage. He also tells Max to insult his boss, which Max reluctantly does.
As the evening continues, Vincent has Max deliver him to more places where Vincent kills people. He has to kill five people by the end of the night. Meanwhile, a Detective Fanning is chasing the two, slowly figuring out what is going on. He pieces together several clues involving the people Vincent has killed, determining that the killer has used the same method to shoot them all; two shots in the chest and one in the skull.
Despite the circumstances, Vincent seems to take a liking to Max, who doesn't return the favor. They later visit Max's mother in the hospital; Vincent wants Max's evening's work to appear as normal as possible to avoid suspicion. Max manages to slip away from Vincent with Vincent's bag, containing his laptop and the identity records of his targets. Max runs over a pedestrian bridge over an expressway and tosses the laptop over the fence where it's run over by a truck. Vincent responds by forcing Max to go to the man, who ordered these hits, a drug dealing gangster, Felix, and retrieve duplicates of the information. Max pretends to be Vincent to the mob boss, and successfully gets the remaining info for the hits. By this time, Fanning has joined an FBI stakeout of Felix's club and identifies Max, whom he thinks is the killer, as a cabbie. Fanning joins the FBI in following the cab. Meanwhile, Felix, questioning his confidence in Vincent, also has him followed by his own men to insure that Vincent will complete the final two hits.
Vincent and Max go to a busy night club to kill a heavily guarded target. The FBI, LAPD, and Fanning also show up; Fanning is looking specifically for Max to escort him to safety. A massive gunfight ensues where Vincent kills his target and saves Max's life. Detective Fanning finds Max and is leading him out when Vincent appears behind him and shoots the police officer.
Max and Vincent escape the carnage and head for the third mark. By this time Max has reached his breaking point and deliberately wrecks his cab. Vincent crawls out and leaves him behind. A police officer approaches Max to help him but sees the bodies Vincent hid in the trunk. While on the ground, Max sees Vincent's new computer screen and realizes that Annie is the final target, which explains why Vincent was outside that particular building earlier; he was studying the building's security systems.
Max overpowers the cop and takes his gun. He races to Annie's building and reaches her at the same time Vincent does. Max shoots Vincent and runs away with Annie. However, Vincent survives his injury and chases the two of them onto a subway train. Vincent and Max fire their guns at one another, with Vincent sustaining mortal wounds. Vincent asks Max if he thinks anyone will notice his body. He dies in a sitting position as Max and Annie leave the train.