The story of an inner-city Los Angeles police precinct where some of the cops aren't above breaking the rules or working against their associates to both keep the streets safe and their self-interests intact.
While the Strike Team ramps up their control of the streets, David tried to crack corruption in the Barn by recruiting Terry to help him take down Vic, only to result in Terry's death. Meanwhile, Dutch and Claudette investigate the murder of Nancy Reborg only to discover her missing daughter has been sold off by her addict father to a child molester.
Internal Affairs investigates the shooting death of Det. Crowley, but Aceveda speaks starts his own investigation. Meanwhile, Claudette and Dutch investigate the shooting of a churro vendor that ends up in the Strike Team busting up a gang initiation
In a routine sweep to nab every outstanding suspect, the detectives divvy up the warrants. But when they cast their nets, they bring up far bigger fish than expected. Danny and Julien uncover a gun-smuggling operation; and Mackey and his team encounter a pro-basketball star who's in town to play the Lakers, when they bust in on drug dealers. Meanwhile, Claudette and Dutch try to catch a man who has been raping women in an attempt to procreate.
Mackey attempts to broker a peace agreement between rival rappers whose feud is spilling into the streets. Danny is attacked after identifying a shooter, Julien helps a woman whose son's body has been stolen, and Dutch and Claudette search for a mission migrant worker. Meanwhile, Capt. Aceveda finds a powerful ally in ""Kingmaker"" Jorge Machado.
David insists that Vic take uniformed cops in with them to bust an Armenian gang's drug delivery. After the bust, Julien sees the Team take a portion of the drugs for themselves. But in the end Shane ends up having the drugs and the vehicle they're in stolen from them. While the search for the drugs and the truck goes on, Mackey learns that his son is autistic.
When the body of a young hooker is found in the district, Dutch and Claudette get the full resources of the Barn for 24 hours and the help of the FBI to search for Dutch's serial killer. Meanwhile, The Strike Force busts an underage prostitution ring, and Capt. Acevaeda continues to investigate Mackey.
When Mackey and Vendrell hook up with a cop from another precinct to investigate the shooting, Vendrell sets off an explosive confrontation with a suspect by making a racial slur. And Mackey seldom a paragon of restraint defuses the situation. But before this tense hour is over, Mackey's complex relationship with Vendrell becomes even more complicated. Meanwhile, Dutch and Wyms search for a serial killer and bring in a psychic on a complaint from the son of one of her clients, and David calls internal affairs after getting Julien's affidavit.
Allegations against the Strike Team are front-page news, and the team is broken up pending the investigation. Mackey threatens to reveal that Officer Lowe is gay if he won't recant his statement about the Strike Team. In the meantime, Vic and Claudette find themselves following the trail of a batch of ""cupid"" meth, while Shane and Dutch try to get along on a case.
A planted gun in a truck-jacking case causes complications for the Strike Team, and now they're left to clean up their own mess. While the rift between Officers Lowe and Sofer deepens, causing Capt. Aceveda to intervene. Also, Detective Wyms deals with the mess of her family during a visit from her daughter.
Mackey helps Connie quit using crack cold-turkey in her desperate attempt to keep her son, leaving Vendrell and Lemansky to investigate a strip-club mugging ring. Meanwhile, Dutch follows his instincts on a serial killer case and Danny is bitten by an HIV-infected perpetrator.
Mackey and the Strike Team mediate a dispute between Rondell Robinson and the Nation of Islam while Wagenbach and Wyms investigate a brutal home invasion in the tight lipped Korean community. Meanwhile, Aceveda revisits his past.
While Vic answers Assistant Chief Gilroy's call for help in covering up a hit and run before Dutch intuits the facts of the case, Shane and Lemmonhead follow the trail of a gunrunner with a penchant for cockfights. Meanwhile, Aceveda turns to Claudette after a double homicide raises ire and fear within an ignored community.
In the aftermath of a riot, cops are being lured into ambush shootings by a rash of bogus 911 calls. Surprisingly Mackey and Captain Aceveda must work together to stop these attacks and solve the problems in The Grove, while Assistant Chief Gilroy tries to pit the two against each other to save his own job.