In Los Angeles, Detective Graham Waters and his partner Ria are involved in a minor collision with a car being driven by Kim Lee. Ria and Kim Lee exchange racially charged insults. Waters later arrives at a crime scene, where the body of an unnamed dead child has been discovered. The film then backtracks 48 hours to trace the preceding chain of events.
Anthony and Peter, two young Black men, carjack district attorney Rick Cabot and his wife Jean. As the men drive away in the SUV, Peter puts a figurine of St. Christopher, the patron saint of travelers, on the dashboard. They pass by Waters and Ria, who are investigating a homicide in a San Fernando Valley parking lot. The pair learn that a white undercover cop, Detective Conklin, shot a Black undercover cop, Detective Lewis, with neither knowing the other was a policeman.
At home, Cabot rails that the carjacking incident could cost him re-election, because no matter whom he sides with, he will lose either the black vote or the law and order vote. Hispanic locksmith Daniel Ruiz overhears Jean, who suspects that Daniel is a gangster, demanding that the locks be changed again.
While searching for the Cabots' stolen vehicle, Sergeant John Ryan pulls over an SUV driven by a wealthy Black couple, TV director Cameron Thayer and his wife, Christine. Though Ryan knows the vehicle is not the one he's searching for, he accosts the couple on his claim he saw Christine performing fellatio on Cameron while he was driving. During the traffic stop, Ryan performs a body search on Christine and molests her in front of Cameron. Ryan's younger partner, Officer Tom Hansen, looks on in horror but does not intervene.
Hansen goes to his superior Lieutenant Dixon to report Ryan's conduct and requests a transfer. Dixon, a Black man, tells Hansen that a racism complaint would hurt his own career and allows the transfer on the condition that Ryan's conduct not be mentioned. Ryan is shown living with his ill father, who cannot get health insurance. On the phone, Ryan takes out his frustrations on the Black HMO administrator he speaks with. When the insurance adjuster does not respond quickly enough, Ryan insults her competency by saying that more qualified white men didn't get her job because of affirmative action.
In the carjacked SUV, Anthony and Peter hit a man of Asian descent while passing a parked van. They take the injured man's body and leave him in front of a hospital. Meanwhile, Waters, who is in a relationship with Ria, gets into an argument with her when he makes a casual remark about Mexico being her country of origin. Ria angrily reminds him that her father is actually from Puerto Rico and her mother is from El Salvador. Waters later visits his mother, who asks him to find his missing younger brother.
Ryan later comes across a car crash and an overturned vehicle. In his attempt to rescue the passenger, Ryan sees it is Christine, who recognizes the officer from their earlier incident and frantically resists his assistance. Ryan manages to pull her out of the car just before it is engulfed by a fireball. As Christine is being helped by paramedics, she stares at Ryan.
Waters is summoned to a meeting with DA worker Flanagan, who tells Waters that Internal Affairs wants Conklin imprisoned. Waters has evidence that Lewis was possibly involved in a drug deal, but Flanagan promises Waters a job as Cabot's chief investigator, as well as the clearing of his brother's criminal record, in exchange for his cooperation. At a press conference, Waters reluctantly confirms the homicide was racially motivated.
Anthony and Peter carjack another Navigator, which happens to belong to Cameron. Cameron fights back and Peter flees the scene before a police car approaches. Cameron and Anthony drive away and a police chase ensues, with Hansen as one of the pursuing officers. When police catch the SUV, Hansen recognizes Cameron, and out of remorse for the earlier traffic stop, he vouches for Cameron to be let off with a warning. Anthony, who was hiding during the exchange, is dropped off at a bus stop by Cameron.
Later that night as Hansen is off the clock, he picks up a hitchhiking Peter. During the drive, Peter reaches into his pocket and Hansen, thinking he is reaching for a gun, shoots him. Peter collapses dead, revealing he was only reaching for his Saint Christopher statuette. Hansen hides the body in some bushes and burns his car. Waters and Ria later arrive at the scene, and it is revealed that the dead body is Waters's brother Peter. Waters's mother disowns him over Peter's death.
Anthony comes across the white van from earlier with its keys still in the ignition. He steals the van and takes it to a chop shop, where it is discovered there are Cambodian immigrants chained in the back. The van had belonged to Kim Lee and her husband (the man Anthony and Peter accidentally hit), meaning they were involved in human trafficking. The chop shop owner offers Anthony $500 per immigrant, but Anthony refuses. After driving the Cambodians to Chinatown and freeing them, he passes by a fender-bender. One driver turns out to be the insurance adjuster Ryan had previously argued with, and the other is an Asian man. An exchange of racially charged insults erupts between the drivers.
