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 Vic searches for his wife and children, the Strike Team allow more drugs into Farmington through a corrupt connection. But when their latest shipment turns bad, the head to Tijuana to uncover the person behind their poisoned cocaine. Meanwhile, Dutch and Claudette try to track down the man responsible for fire necklacing the captains of two separate gangs.
As Vic gets closer to finding his family, the Strike Team focus their attention to Armadillo after he burns down Tio's HQ. Now Vic must prevent Claudette from finding out the truth about his connection to Tio and his men. Meanwhile, Dutch is followed around by the new civilian auditor to solve a meter-maid murder, and Danny and Julien try to clear up issues between feuding neighbors.
Still fuming from the death of Tio and his brawl with Armadillo, Vic takes a day off and leaves the Strike Team with Aceveda, only to end up helping an old partner bust the man who helped him lose his job. Meanwhile, Dutch and Claudette search to find the people behind the torture and mutilation of a woman who may still be alive, and Julien fails to back up Danny's side of the story from her shooting.
Now that Vic is back to work, he and Shane go undercover as dirty cops to find the man behind a robbery/murder. Meanwhile, Dutch and Claudette track down an old rival of Claudette's after a turned in gun is connected to a previous case. And in an attempt to get the Asian vote in the election, David assigns Julien and Danny to watch over a Korean parish.
David works with Vic and the Strike Team to take down a dealer giving heroin to school kids, while Dutch and Claudette help a woman find her Alzheimer addled mother.
Detectives Wagenbach, Mackey and Wyms investigate a massacre at a women's shelter, and Captain Aceveda works with Lowe on the case of a stolen bicycle.
Vic and Emma try to help a woman who's in an abusive relationship. Vic and the Strike Team begin to make plans for the money train take down, even though the greenlight still has them on their toes. When David tells Dutch that he embarrassed the department with the Bob and Marcy case and that Claudette is now lead on all their cases, he's forced to take any action necessary to prove himself in a new homicide. Danny finally makes a stand against Yassirah.
When Vic discovers that Ronnie has been burned as payback, the rest of the team does everything they can to put an end to him. Meanwhile, Claudette makes headway on her investigation against Vic after a conversation with Corrine, and Dutch takes Danny under his wing as they try to find the suspect of a Thai Town beating.
Flashback to the first day of the barn. Under pressure to get results, Vic and his new Strike Team make an impression on the streets. Dutch and Claudette realize they make a good team, and David discovers he doesn't have as much power as he thought he would.
When Lanie's report on the Barn is leaked to the press, everyone suddenly fears for their jobs, including David who's mentioned as the reason for most of the problems. Gilroy skips bail and winds up on Vic's doorstep looking for help, so while Vic and Shane deal with him Lemonhead is forced to show the newest member of the Strike Team the ropes. Meanwhile Claudette faces some of her own demons as she and Dutch try to uncover the culprit behind a possible robbery/homicide and Danny comes to a startling realization.
With Ronnie's face healed he comes up with a plan to take down the Money Train, and the Strike Team is all in. Unfortunately, a federal criminal comes back to Farmington, and the Team has to use every connection trick, and resource to bring him in to prove the Barn is still a force. Meanwhile, Dutch and Claudette investigate the rape of a young girl which leads to information that puts the case in a new light. Plus, an old friend from the past reappears to make Julien's life hell.
While the Strike Team puts the finishing touches on the money train take down, Vic goes it alone and works with Dutch and Claudette to find a missing kid. David gets an unwanted visit from the Chief and Julien receives an unpleasant surprise.
When a gang execution hits close to home for Claudette, Vic, Tavon, and Dutch work together to find the culprit before anyone else gets hurt. Shane, Lemonhead, and Ronnie are forced to choose between hitting the money train without Vic or letting it go. Meanwhile, Danny receives some life changing news and Julien's harassment reaches a whole new level.