Vic is no longer the cop he used to be, acting adrift after his past actions have caught up to him. The strike team has been dissolved, leaving Mackey to menial busts that keep him off the streets. When Aceveda moves on to his new City Council position, Captain Monica Rawling takes over the Barn and empowers Vic to implement her controversial anti-gang policies.

Mackey tries to help an old acquaintance find a wayward teenager, but the search quickly turns ugly when the missing teen appears to have been involved in a shoot-out. Meanwhile, Shane heads out into the field with his new partner Army, teaching him shady police tactics and seeing how far he'll go to be partnered up. Plus, Aceveda spends his last day trying to bury Vic for good, which makes things difficult for Rawling trying to take his place.

With Farmington on the brink of a gang war, Monica and Vic race to find the catalyst and stop the bloodshed, enlisting Antwon's help along the way. Still in the doghouse, Dutch decides to take action in thawing the relationship between Claudette and the D.A. Danny and Julien get up close and personal with the Farmington 1-Niners, while Monica looks to Vic for support when the implementation of her property seizure policy challenges her morality.

When Monica puts Vic on the trail of an escaped fugitive in Farmington, he must continue to prove his worth while playing it straight. Claudette gets suspicious of the D.A's motives when she and Dutch are assigned to investigate a major drug dealer who ends up being a minor offender. David seeks an illicit outlet for the troubling feelings caused by his rape. Vic decides to bring Shane closer as his fears about Shane's connection to Antwon Mitchell rise.

A tip from Lemonhead's juvie would leads Vic and Monica to take down a major heroin operation with connections to Antwon Mitchell. Monica continues to battle Aceveda as she tries to sell her new policies to the community, and Julien begins to doubt her methods. Claudette loses trust in Dutch when she suspects he made a backroom deal with the D.A. And Shane and Army find themselves over their heads with Antwon when he blames them for Vic's heroin bust.

Vic and Monica stake a deal with the DEA to shut down Mitchell's tar heroin operation. When the bust comes up empty, Vic's suspicions of Shane grow, until Shane proves himself by coming up with a key piece of evidence that reveals a large stash of tar being stored at a local church. Meanwhile, Dutch and Claudette's friendship continues to feel strain as they try to tie a young woman's murder to a suspected serial killer. Plus, Julien takes a stand against Monica's policy, then goes to David for support when she suggests he consider transferring out of Farmington.

Just as Monica and Vic get close to a big break in the Garage Sting, Chief Phillips unexpectedly hands over the bust to the Organized Crime Unit. He blames the decision on an emerging PR scandal involving a videotape of Vic at the church bust that was leaked to the Assistant Chief through Aceveda's office. Vic uses his leverage with the Byz Lats to find a Russian mob leader before the mobster flees the country. Monica threatens two foster care social workers with jail after a young girl is found close to death in her foster home, then tells Julien if he doesn't put in for a transfer, she'll request one for him herself.

Monica and Vic rush to get their informants off the street after two C.I's are found brutally murdered. Meanwhile, as Dutch and Claudette investigate a brutal beating and robbery, a case from the past forces Dutch to take one in the line of duty. Plus, Vic suspects he's being set up when Shane comes to him after his situation with Antwon and Halpern spins out of control.

Monica orders her units to turn the streets of Farmington inside-out when two officers mysteriously disappear after answering a 911 call. Shane tries to make amends with his old crew after Vic agrees to help him get out from under Antwon, but things don't work out as planned. Dutch and Claudette convince Monica to let them take active roles in the case of the missing officers, but soon find themselves at a dead end with the only witness being clinically insane.

Vic and Monica go head to head with Antwon, and do everything in their power to get him to admit to being involved with the cop killings. Monica is shocked when Vic and Shane confront her with the information they've been hiding regarding Antwon and Angie's body. Shane and Army wonder if they'll be able to pass the lie detector test Monica is forcing them to take. Meanwhile, after another young black woman is murdered, Dutch and Claudette hope to prove their suspicions correct with their recently relocated Texan.

Vic and the Strike Team use their leverage on the One-Niners to track down anyone involved with the cop killings. Their hunt leads them down an unexpected path with the Russian mob. Monica puts pressure on the team to come clean about any of their dealings with Antwon. Dutch and Claudette investigate a gang shooting and soon realize their key witness is close to the Barn, and has something to hide.

Vic and his crew track down the Russian who was involved with the cop murders, but they lose control during his interrogation and the hit man dies in an explosion before they can get any answers. Meanwhile, Aceveda is blackmailed by the man who assaulted him. Plus, Rawling's seizure is on the verge of being shelved.

Monica, Vic and the strike team work together to put Antwon Mitchell back behind bars after his deal with the DEA released him from prison. When Vic reveals his suspicions of David's connection to both Antwon and an inmate's murder, David must protect his political future at any cost. When the murder of an over-protective father leads Claudette and Dutch back to a foster home they had previously investigated, Monica makes an unpopular decision that helps seal her fate.

As racial tension in the area escalates, the Strike Team attempts to end a race war, while Claudette and Dutch investigate a riot at a high school. Meanwhile, an Internal Affairs officer begins his investigation of Vic and the Strike Team by first zeroing in on Lem. A pregnant Danny refuses to reveal the identity of the father, and Julien begins training a rookie cop named Tina Hanlon.

During an interrogation, Kavanaugh reviews the Strike Team’s corrupt past and attempts to weaken Lem’s loyalty to Vic by bringing up the connection to Terry’s murder. Meanwhile, the Strike Team investigates a multiple homicide. Dutch and Claudette suspect that a minister might have been involved in an attempted murder. Tina gets in over her head while on duty with Julien.

The Strike Team tries to develop a strategy to deflect the Internal Affairs investigation as Vic finally comes face to face with Kavanaugh. Meanwhile, Tina goes undercover to help take down a sex-trafficking ring; and friction between Claudette and Dutch deepens when she reopens one of their past cases.

With the IAD investigation in full force, Vic seeks legal representation from Becca Doyle for the Strike Team. Also, a suspicious Vic decides to confront Emolia after he begins to doubt her loyalty to him. Meanwhile, Dutch and Claudette investigate the ghastly murder of a pregnant woman. Tina continues to make mistakes while on duty.

Via a bug planted in the clubhouse, Kavanaugh monitors the Strike Team as they investigate an illegal prescription drug ring that is proving to be deadly for the people of Farmington. While working on a missing person’s case, Dutch attempts find out what Claudette is hiding.

As the Strike Team is preoccupied with gang violence, Kavanaugh decides to make the Barn his base of operations. An evasive serial killer from Dutch and Claudette’s past reenters their life. Meanwhile, additional strain is placed on their working relationship when Tina learns something personal about Julien.

Claudette further aggravates her illness as she continues to aggressively interrogate Kleavon Gardner. The Strike Team works with the Chief of a citywide task force to investigate the murder of a drug dealer’s girlfriend and her daughter. Meanwhile, Kavanaugh attempts to discover how Vic acquired the $65,000 that was given to Corrine, and Ronnie is up next for questioning in the IAD investigation.

Kavanaugh seeks the help of Antwon Mitchell in his ongoing quest to take down the Strike Team. In the midst of this, Kavanaugh has a lot on his mind as his ex-wife reenters the picture, and he reluctantly agrees to let Vic send Emolia undercover to infiltrate a Salvadoran gang that is stockpiling grenades.

The Strike Team attempts to make bail for Lem who is now in jail, but they discover that Kavanaugh has frozen their accounts. Claudette returns to work to help Dutch investigate the murder of a man who’s body was found in the dumpster. Meanwhile, Tina jeopardizes her future at the Barn after she endangers the life of an undercover detective. Corrine confronts Danny about Vic’s unfaithfulness and the identity of the baby’s father.

To the dismay of his friends, a weary Lem is thinking about accepting a deal from the D.A. where he has to plead guilty to the heroin charges. With no other choice, Vic reluctantly meets with Antwon in order to ensure Lem’s safety in prison. Meanwhile, unforeseen circumstances that are beyond Claudette and Dutch’s control might cause irrevocable damage to their friendship.

As Vic prepares to help Lem get out of the country to begin a new life in Mexico; Kavanaugh and Aceveda attempt to capitalize on the situation by using this as means to try to take down the leader of the Strike Team. Dutch decides to file for a transfer. Meanwhile, Shane tries to cut off the investigation by taking extreme measures and Danny finally confronts the father of her child.

With the Barn grieving over the loss of one of their own, Vic's out to avenge his friend's murder, but finds himself in the crosshairs of Kavanaugh. Claudette assigns the Strike Team to investigate the torching of a methadone clinic. Meanwhile, Julien and Tina look into a robbery/assault at a porno shop, and Dutch makes a horrifying discovery in San Marcos.

Kavanaugh acquires what he needs in order to apprehend Vic who is preoccupied with getting revenge on Guardo. Claudette finds herself under the political microscope as a result of the San Marcos incident, and Danny receives some news about her future at the Barn.

Consumed by bloodlust, Vic finally gets the chance to avenge his friend's murder, despite Shane's pleas against it. Meanwhile, Ronnie is assigned by Claudette to help Dutch and Billings investigate a robbery homicide at a pharmacy.

Claudette gives Vic a chance to save his job if he agrees to train his potential replacement. An unsolved rape case from the past that Dutch and Claudette were working on resurfaces. Meanwhile, Aceveda meets someone that can help him further his political career.

After being badly beaten, Shane's life spirals even more out of control as his guilt continues to eat away at him and his marriage begins to fall apart. Vic and Ronnie try to learn who was responsible for Shane's attack. Meanwhile, under the new leadership of Kevin Hiatt, Claudette assigns the Strike Team to investigate the San Marcos murders. Dutch and Billings make progress in a serial rapist case.

Vic redirects his attention to finding out who really killed Lem after he learns for certain that Guardo wasn't involved. The Strike Team investigates the murder of a politician's daughter. Later, Cassidy confronts her father about his unethical past.

After Vic disowns him, Shane turns to the Armenian mob for help. Vic gets more involved with the San Marcos investigation, while Dutch and Billings are able to track down someone who survived the massacre.

Vic learns about his true status at the Barn from Hiatt. Shane gets involved with the daughter of an Armenian mob boss. Claudette begins to question Hiatt's loyalty.

As progress is being made in the San Marcos investigation, Vic receives bad news about his career. Meanwhile, Shane and Diro become business partners as she prepares to take over the Armenian mob.

Claudette notices Hiatt's mistake when he makes an arrest, and Billings delivers shocking news to the department. Vic forms an alliance with Aceveda, while he waits for his review board hearing. Meanwhile, Shane's life keeps spiraling out of control.

Vic challenges Shane and deals with threats to his family; a federal agent arrives in Farmington to investigate a recent wave of violence.

As a local gang war heats up, Vic positions himself as a valuable commodity to the warring parties; Corrine and Cassidy confront Vic.

Vic works an angle to make himself valuable to the Armenian mob; Corrine finds herself in a surprising legal jam; Tina targets a producer of adult entertainment.

The gang war erupts in unexpected ways that Vic cannot control; Dutch and Billings' homicide investigation grows into something more disturbing; Cassidy reaches out to Danny.

Claudette encounters a murderous old nemesis; Vic confronts Olivia about her political connections; Dutch's case gets personal.

Vic sets into motion plans to end the gang threat as his relationship with Cassidy deteriorates; Dutch and Billings investigate a possible sleepwalking murderer.

A prostitute from Vic's past is the key to taking down a violent drug dealer; Dutch worries about Claudette's health; Danny takes drastic measures to protect her child.

A local priest may be protecting drug dealers; Dutch and Billings close in on attempted cop killers; Corrine learns uncomfortable truths about Vic.

Vic closes in on Shane, Mara and their sick young son; Claudette dismantles the Strike Team; Pezuela offers Acevada "assistance" for his mayoral campaign; Rita Denton (Frances Fisher) comes on to Dutch; and Billings' ex-wife and daughter are fearful when a registered sex offender moves into their neighborhood.

While Shane remains holed up in L.A. with Mara and Jackson, Corinne decides to cooperate with Dutch and Claudette, who's now spearheading the LAPD effort to bring down Vic. Meanwhile, Vic plays Aceveda, Pezuela, Beltran and ICE against each other. But Ronnie's tempted to simply give up and run to Mexico. "And you should run too man" he tells Vic.

Corrine agrees to be Vic and Shane's go-between and also agrees to cooperate with Claudette and Dutch as she does so. Meanwhile, Vic comes to an understanding with Aceveda and seeks one out with Olivia; and Claudette assigns Ronnie to work with Julian to investigate the murder of a high-school football star, keeping Ronnie out of the barn and unable to intercept the letter Shane sent to Claudette detailing the Strike Team's "sins."

Olivia joins forces with the Strike Team to catch a Mexican drug king and his shipment. Meanwhile, Dutch cleans up Billings' mess, and the death of a woman associated with the Strike Team prompts an investigation by Claudette.

Officers in the Barn investigate a woman's disappearance and the arrival of a large drug shipment; lives change forever.