Detectives August Brooks and Chase McDonald meet when August and several officers are being overwhelmed by criminals in an explosive shootout. Chase arrives in his Porche and immediately neautralizes the situation with a grenade launcher. Moments later, August discovers that Chase is his new partner, and they are immediately assigned the case to track down a bomber - nicknamed the Daybomber - who has set off a series of explosions in his quest to warn people of the advances of technology.

Chase and August are at August's gym, where they are volunteering their time to help keep kids off the street and out of gangs. In the boxing ring is Andre, a young fighter determined to stay away from gang violence. But when word comes in that Andre's brother has been shot and killed by a rival gang, Andre swears to avenge his brother's death. Chase and August try to persuade him to let the police handle it, but Andre slips from their grasp in pursuit of the killer. The incident also brings back memories for Chase, who is struggling with unresolved guilt over his former partner's murder by a gang youth.

Chase and August are escorting an annoying accountant named Cecil Rusk - the star witness for the prosecution in mobster Marius Roma's tax evasion trial - to court when they are ambushed by Roma's brother and his thugs. After their car is destroyed, the trio escape on foot through a hail of gunfire. Alone on the streets of Los Angeles, they decide to head out of town, where they believe they'll be safe. But a mole inside the force is leaking information on the detectives' whereabouts to Roma's mob, and it's up to Captain Jensen and Det. Richardson to figure out who it is.

Ariel, a prostitute, is found dead. Nearby, a beautiful young hooker named Electra wanders the streets in a daze. Narrowly escaping Uzi-toting hitmen, she is taken into custody by Chase and August. Electra has amnesia and cannot remember what happened the night of Ariel's murder. Eager to crack the case, Chase and August are relieved of their investigation by Captain Jensen after orders from the mayor's office. Chase, convinced there is a cover-up in progress, refuses to drop the case.

When a group of criminals rob a computer chip assembly plant, Chase and August link the six million dollar heist to a local computer store. Posing as computer industry executives, the detectives visit the store and stage a robbery, pretending to save the day. Winning the confidence of the store's owner, Ray Bernard, they begin to work their way into his group.

Playing host to a COPS-like television show, Chase and August are out to catch the gangbangers responsible for a string of 211s around the city. The two-person TV crew tags along while the detectives tackle a 211 in progress and apprehend a couple of suspects. When Chase saves a store owner's 12-year-old boy just before a grenade erupts and the producer of the show says he plans to make Chase ""a star,"" August fears his partner's desire to be a movie star will slow their investigation.

Chase and August are eyewitnesses to a young man who throws a Molotov cocktail into a car right outside the gym. The perpetrator gets killed in the ensuing pursuit, but they find out that the car was registered to Carlos Altamarino, a known drug dealer. Chase is visited by an old college friend, now a CIA agent, who gives Chase a mysterious gold key for safekeeping and reveals that Carlos' operation has shifted power to a brother, a cousin, or perhaps even Carlos himself using an alias. The new boss carries the name Charlie Altamirano. Chase's friend is killed later, and the detectives work to figure out just what exactly is going on.

A young female tourist has been brutally murdered. The detecives suspect ""the Reaper,"" a deranged man who suddenly appears on the roof of the crime scene, screams biblical quotes at the officers, and opens fire. After a rooftop pursuit, Chase and August take him into custody. At police headquarters, Jensen explains that ""the Reaper"" is merely a mental institution escapee. The killer is still on the loose and plays with the detectives by leaving behind verses of a poem.

Arriving at the scene of a murder, Chase and August find that the victim is Bobby Roman, a favorite target of controversial shock-jock Jerry Maxwell. Roman has been shot in the head, just as Maxwell always advocated. When Chase and August confront Maxwell about the murder, the beligerent radio host denies involvement in the crime. But then a call comes into the station, and Maxwell is shocked to hear a devoted listener, Ward Valasco, claim that he killed Roman, and that he intends to kill all of Maxwell's enemies.

Arriving at a crime scene, Chase and August find a member of the Bulldog Crips gang shot to death. Chase is surprised to find a note containing rap lyrics pinned to his sleeve, which leads them to a rival gang member named Cage. After a daring chase, Cage is apprehended and interrogated by the detectives. Cage accuses A.K., a famous rap star, of the murder. Kicking in A.K.'s door, Chase and August square off with the musician and his manager, Frank Millan. But the detectives soon learn that nothing is what it seems, and the real killer is closer than they think. Meanwhile, Jodi's parents are in town.

When a wealthy foreign couple touring L.A. are found murdered and robbed, Chase and August are assigned to investigate. What they don't know is that these are not random killings, and that Russian mobster Ivan and his gang are plotting more crimes. The FBI demands that Chase and August focus only on the homicides and leave the robberies to them, but the detectives believe the two crimes may be connected.

A promising young boxer is beaten and left nearly dead. Arriving at the hospital, August and Chase intercept a hitman who attempts to finish the kid off with a lethal injection. They pursue the would-be killer through the hospital, finally stopping him with a jolt from a set of defribulator pads. Immediately, they sense that this case involves more than a random beating. August is visited by his former boxing coach, Frank, to whom he hasn't spoken since their falling out many years before. Frank says that he must tell August a secret that has been haunting him. But before he can reveal what he knows, Frank turns up dead, plunging the detectives further into mystery.

After a car chase with police, young Joey Morello, brother of a New York crime boss, barricades himself within a road-side burger stand, takes hostages, and demands a bus, plane, and money for an escape. Chase gains Joey's trust and talks some sense into the young man, getting him to drop his weapon. But when the cook panics and tries to escape, Joey is startled and draws an ankle-gun, and Chase is forced to shoot. The young kid dies, and his crime boss brother arrives in L.A. looking for revenge. Meanwhile, Chase is targeted by an Internal Affairs officer who is convinced he shot the young man for no reason because the kid's ankle-gun could not be found.

Chase and August thought they'd seen it all until they learn that the latest crimewave involves stealing kidneys from unsuspecting citizens. Racing to a downtown motel, they meet Andrew Green, the latest victim of the bizarre scheme. As Green is wheeled to an ambulance, he spots the prostitute who lured him to the scene of the crime where he was drugged and operated on, and Chase and August take off in pursuit. Det. Maria Vallejo goes undercover as a prostitute to assist in the detectives' investigation.

A van filled with illegal Mexican immigrants crashes in a violent explosion, killing many of its stowaways, and Chase and August arrive on the scene. Survivors limp with cuts and bruises, but the smuggler, the Coyote, has disappeared. One of the survivors tells the detectives that a man named Delgado had smuggled them across the border. Det. Maria Vallejo connects Delgado to a suspected sweatshop owner, and the detectives reluctantly put her undercover.

An abandoned church near August's home explodes into a fireball, triggered by an illegal methamphetamine lab. The next morning, he and Chase confront a group of bikers while trying to arrest one of them, and the bikers' trailer erupts into flames. It was being used as a meth lab. It's apparent somebody wants the labs out of business. Determined to crack the case, the detectives team up with Annie Mason, a new forensics assistant at police headquarters. Annie is able to turn up a suspect, a dangerous biker called the Falcon, with a rapsheet a mile long. But when he checks out the man's file, August is shocked to recognize the Falcon as Robert Hatcher, his former partner.

A car bomb explodes, killing the Vice President of Sawchuck Industries. In their search for suspects, Chase and August meet Meredith Nowell, a beautiful young volunteer at Green Planet, an environmental protection league. Meredith reveals that Sawchuck Industries had been dumping deadly toxins, which infected Los Angeles groundwater, killing a mother and daughter. When another Sawchuck executive is killed in an explosion, the detectives begin to suspect Joshua Duncan, the man whose wife and daughter died of cancer as a result of the poisoned water.

Teenagers Alan and Ian cruise down a city street smashing mailboxes, while Harold's younger brother, Ian, is forced to videotape their antics. The two older kids' thrill-seeking escalates when they smash the window of a store and accost the cashier. When the cashier opens fire, both he and Ian fall to the ground, and the other two take off running, Harold throwing the video camera into a dumpster before being caught by police. August and Chase question Harold at headquarters, but he has been threatened by Alan not to talk, or he and his mother will be killed.

Chase and August arrive at the scene of a murder on quiet Lily Lane, where Sheila Hanson has been stabbed to death in the bedroom. Her husband says he returned home to find his wife dead and a man robbing the house. The detectives chase after the perp and are shocked to find that it is David Jackson, a kid who belongs to August's gym and denies killing anyone.

Prisoners are being beaten to death at El Toro Prison. Guard Larry Clark plans to go to the authorities, but before he can talk, a bomb rips through his house, killing him and his wife. Chase and August suspect that Warden Brinkman is involved in setting up to-the-death fights between the inmates. Determined to crack the case, August goes undercover in the prison, but his cover could be blown when it's learned that Robert Hatcher, his former partner, is being transfered to the prison.

Art thief Richard Turpin, known as the Gentlemen Bandit, crawls through the skylight of a Los Angeles museum, only to be caught in the act by Chase and August, who apprehend him and haul him off to jail. The British government decides to extradite Turpin, accusing him of association with a radical faction of the IRA. Scotland Yard detective Wilhemina ""Willy"" Smythe arrives to collect Turpin, but her plans are soon thwarted when a terrorist named Riley shows up, who has plans of his own for the thief.

Chase and August arrive at the scene of a murder at a mental hospital, where a prominent psychiatrist has been stabbed to death. The suspect is a patient, Treat Donnelly, who is revealed to be Chase's cousin and vehemently denies killing the doctor. Several of Dr. Benning's colleagues fall under suspicion, and the plot thickens when it is learned that Elaine Hall, the dead doctor's beautiful assistant and one of the suspects, has more than one personality.

When former stars of the popular 1960's television show ""Captain Crimestopper"" are murdered, August suspects the show's star, out-of-work actor Wayne Berry, but Chase refuses to believe that one of his childhood heroes could be a murderer. At one of the crime scenes, the detectives apprehend a man disguised as the superhero, who turns out to be Berry himself, intent on finding the killer. When forensics concludes that Berry is not the killer, the actor is released, but an attempt on Berry's life at an autograph-signing puts the detectives on the trail of the one responsible.

Chase and August investigate a gun-running operation in which the prime suspect turns out to be recently-murdered CIA operative James Camden. Chase is seduced by Camden's former partner, but the romance is cut short when he discovers she may be involved with the plot as well.

Leonard Murdoch, a scientist for the high-tech firm Biotech, is murdered, and Chase and August suspect someone in his company wanted to keep him quiet. The detectives get a call from a Biotech whistleblower who tells them that the firm's CEO is planning to sell a top-secret biological chemical to international American enemies. Chase is convinced it's a cover-up for a government study of alien DNA, but before he and August can learn more, they are surrounded by military vehicles and men in black.