Set in Los Angeles, the film opens following a car accident involving detective, Graham Waters (Don Cheadle), Ria (Jennifer Esposito), his partner, and Kim Lee. As Ria and Kim Lee exchange racial insults, Waters gets out of the car and investigates the crime scene which had indirectly caused the accident after identifying himself as a detective to the officer in charge. Waters sees the victim's shoe lying on the ground and then stares at something off screen which horrifies him. One day prior, a Persian man, Farhad (Shaun Toub), and his daughter Dorri (Bahar Soomekh) are buying a gun, but the shop's owner refuses to sell to them due to their race. Ultimately, an infuriated Farhad is escorted outside. Dorri completes the purchase and chooses an unspecified type of ammunition, while enduring verbal sexist harassment from the shop owner.
In another part of town, Rick Cabot (Brendan Fraser), the local district attorney, and his wife, Jean (Sandra Bullock) are carjacked by Anthony (Chris "Ludacris" Bridges) and Peter (Larenz Tate). Detectives Waters and Ria arrive on the scene of a shooting between two drivers outside of a store. The surviving shooter is a white male identified as an undercover police officer. The detectives learn that the dead shooter, a black male was also a police officer. Afterwards, at the Cabot house, Daniel Ruiz, a Hispanic locksmith (Michael Peña) is changing the locks. He overhears Jean, who is frustrated having felt nervous about the two black men but refrained from saying anything to avoid appearing racist. She instructs Rick to hire another locksmith in the morning, believing Daniel to be a gang member.
LAPD Officer John Ryan (Matt Dillon) and his partner, Tom Hansen (Ryan Phillippe) begin their evening patrol. They pull over a Navigator similar to the one carjacked earlier, despite discrepancies in the descriptions. They order the couple, director Cameron Thayer (Terrence Howard) and his wife Christine (Thandie Newton) to exit. Cameron is cooperative, but Christine is argumentative. An angry Ryan sexually molests Christine under the pretense of administering a pat-down. Intimidated, Cameron says nothing. When Ryan finishes, the couple is released without a ticket. The next day, Hansen talks to his superior, Lt. Dixon (Keith David) about switching partners. Dixon, a black man, claims that Hansen's charge of Ryan as a racist could cost both Hansen and Dixon their jobs. Dixon suggests a transfer to a one-man car and mockingly tells Hansen that he should justify it by claiming to have uncontrollable flatulence.
At the Thayers' house, Christine is enraged that Cameron did nothing while she was violated. Cameron insists what he did was correct, and the argument ends with Cameron storming out. At his home, Daniel talks to his daughter, Lara, who is hiding under her bed after hearing a gun shot. To comfort her, Daniel gives her an "invisible impenetrable cloak". He then puts her to bed and then gets a page for another locksmith job. In the carjacked SUV, Anthony and Peter, distracted by their argument about racism, pass a parked white van hitting something. Getting out, they see that they have run over an Asian man. Unsure as to what to do, they eventually pull him out from under the car and dump him in front of a hospital.
At Farhad's shop, Daniel replaces a lock on the shop's back door. He tells Farhad that the door is defective and he needs a replacement. Farhad accuses Daniel of cheating him, and refuses to pay. Daniel crumples up his work order and throws it away, leaving irritated. The next morning, Farhad discovers that his store has been wrecked and tagged with racist graffiti. Later, an insurance adjuster tells Farhad that his insurance won't cover the damage, calling it a case of negligence as he had been advised to replace the door. Farhad vows revenge, but the locksmith company won't tell him Daniel’s name. He later discovers the address through the discarded work order.
Ryan visits Shaniqua Johnson (Loretta Devine), an insurance representative with whom he argued earlier. Apologizing for insulting her in their prior conversation, he explains that his father was diagnosed with a bladder infection but fears the diagnosis is incorrect and that it may be prostate cancer. Ryan wants him to see a different doctor, but is told that their health plan won't cover it. Coldly, Ryan tells of his father's acts as one who employed black workers when others wouldn’t. He explains that his father’s business was destroyed when the city began to show preference to minority owned businesses. He suggests that Shaniqua has benefitted from the same type of affirmative action, and begs her to help his father who lost everything so that people like herself might advance. Insulted, she responds that his father sounds like a good man, and that if he had come to the office she might have approved.
Waters goes to visit his mother, a junkie who lives in a small apartment. She asks him to find his younger brother. Waters promises to find him, and notices the lack of food in the apartment before leaving. Outside, he lies to Ria and tells her his mother wasn't home. In the studio where Cameron works, a white producer suggests that a black actor isn't acting "black" enough. Cameron thinks he's kidding, but decides to re-shoot the scene. Christine then arrives and wants to talk about the previous evening, saying that she resented the loss of his dignity the night before. Cameron refuses to speak about it and she leaves in tears. Christine is involved in a car accident and trapped inside her overturned car. Ryan is one of the officers who responds to the accident. Upon recognizing Ryan, Christine screams for him to leave, but he is able to get her to agree to allow him to rescue her. With the assistance of his partner and spectators, Ryan manages to pull Christine out just as the car bursts into flames. A grateful but confused Christine looks back at Ryan as she is taken away.
Driving alone in his Navigator, Cameron comes to a stop sign. Anthony and Peter try to carjack him, realizing too late that he is black, having previously stated that they never robbed black people. Cameron fights back, drawing the attention of some nearby cops. Peter flees as Cameron and Anthony take off in the car. After a chase, the car is cornered. Furious, Cameron gets out and becomes belligerent, while Anthony hides in the passenger seat. Hansen, who responded to the call, recognizes Cameron and talks him down. When they are released, Cameron calls Anthony an embarrassment and sends him away. Farhad confronts Daniel when he returns home and threatens him with his gun, demanding money. Seeing this, Lara runs out to protect him with her "cloak", just as the shot is fired. Miraculously, the little girl is okay. Daniel carries his daughter away, crying along with his wife as Farhad leaves, confused.
Still distraught over her carjacking and finding her friends unsympathetic, Jean slips and falls down some stairs. She is later taken to the hospital by her Hispanic housekeeper, Maria. Jean, who has berated the woman a number of times, is overcome. She embraces Maria, calling her “my only friend.” While hitchhiking, Peter is picked up by Hansen, who is off-duty. They chat, but then start to argue; Peter claims to appreciate country music and hockey which Hansen interprets as mockery. Peter laughs at a dashboard statuette of Saint Christopher at which point Hansen pulls over and demands that he exit. Believing that his passenger is pulling out a weapon, Hansen shoots and kills him. Peter’s hand falls open revealing his own statuette of Saint Christopher.
The narrative then returns to the movie's opening scene with Waters at the accident scene and Peter is revealed to be Waters' missing brother. Waters’ mother identifies Peter’s body at the morgue and Waters promises to find who is responsible for Peter's death, but his mother tells him she already knows that he killed his brother because he failed to find him as she asked. Dorri comes to see Farhad, who explains what happened. He thinks that the little girl was his angel and tells Dorri it's going to be okay. Dorri removes the pistol and ammunition revealing them to be blanks. Hansen abandons his car and sets it on fire to destroy the evidence of his crime. Cameron later finds it when a few locals are treating it as a bonfire and throws a block of wood into the blaze as it begins to snow. Christine calls him and they forgive each other.
Anthony inadvertently returns to the white van from earlier. Finding the keys still in the door, he drives the van away. Kim Lee (the Asian woman from the crash at the film's opening) arrives at a hospital looking for her husband, the man Anthony and Peter hit. Still coherent, he tells her to cash a check that he has in his wallet. Anthony takes the white van to a chop shop, and finds a number of Cambodian immigrants locked in the back of the van, revealing that the Asian man was in fact smuggling slaves. The shop owner offers $500 for each. Anthony refuses and takes the slaves to Chinatown where he releases them.
Nearby, another minor fender-bender occurs involving Shaniqua and another foreign-born driver. They start insulting each other as the snow falls.
