Graham Waters (DON CHEADLE) is a detective in Los Angeles, a sprawling city filled with people of different races and ethnicities, as well as unresolved racist beliefs, attitudes and actions. He and his partner and lover, Ria (JENNIFER ESPOSITO), have just been involved in a car accident where such attitudes surface. Yet, he's more interested in a recently discovered body along the side of the road, unaware of the events from the preceding day that led him to his place.
It starts when thugs Anthony (CHRIS "LUDACRIS" BRIDGES) and Peter (LARENZ TATE) carjack the district attorney, Rick (BRENDAN FRASER), and his wife, Jean (SANDRA BULLOCK), who's upset that societal pressures prevented her from acting on her gut instinct to avoid the two men. Officer Ryan (MATT DILLON) of the LAPD has no such hesitations, however. Upset with what he thinks equal rights have done to the country and his father - not to mention thinking his pop's getting the cold insurance shoulder from black HMO worker Shaniqua (LORETTA DEVINE) -- he takes out his anger on black TV director Cameron Thayer (TERRENCE HOWARD) and his wife Christine (THANDIE NEWTON) during a traffic stop.
His young partner, Officer Thomas Hansen (RYAN PHILLIPPE), is uncomfortable with Ryan's racist actions, but their black boss, Lt. Dixon (KEITH DAVID), won't do anything about it. Also harboring and encountering racist feelings is Farhad (SHAUN TOUB), an Iraqi shop owner whose daughter, Dori (BAHAR SOOMEKH), is upset with him for having recently purchased a handgun. When his shop is broken into and ransacked, he thinks locksmith Daniel Ruiz (MICHAEL PEŅA), father to 5-year-old Lara (ASHLYN SANCHEZ), is responsible since Farhad didn't take his advice to fix a broken door.
As their various stories intersect throughout the day and night, various forms of racism repeatedly rear their ugly heads, eventually leading to an act of violence that leaves one person dead.