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

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.

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.

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.

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

When Aceveda confirms that the Strike Team is the target of an Armenian mob hit, Mackey must take matters into his own hands. Meanwhile, Whym's career is on the line when she disobeys Aceveda's orders to put a case to rest that may prove the innocence of convicted felons.

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.

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 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.

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.

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.

In the aftermath of a riot, cops are being lured into ambush shootings by a rash of bogus 911 calls. Vic and Aceveda are forced to work together to stop the attacks and solve the problems in the Grove, while Gilroy attempts to pit the two against each other in an effort to save his own job.

With an Armenian hit-man hot on their trail, the Strike team sweeps the streets of the Armenian community to find him before he finds them. After catching a break, Aceveda's suspicions grow about the Strike Team's involvement with the Money Train robbery. Meanwhile, Dutch and Claudette investigate a case that could repeal hundreds of convictions, which leaves Claudette having to choose between her conscience and her career.

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.

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.

As Vic gets closer to finding his family, the Strike Team focus their attention to Armadillo after he burns down Tio's business, an act that threatens to expose Vic's protection racket. As Claudette gets closer to the truth about Vic's connection to Tio, Dutch is accompanied by the civilian auditor to solve the murder of a meter maid, while Danny and Julien intervene between two feuding neighbors.

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, Lem, and Ronnie are forced to choose between hitting the money train without Vic or letting it go. As Aceveda prepares for the city council election, Danny receives some life-changing news, and the harassment inflicted upon Julien reaches a whole new level.

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.

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.

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

As Dutch uncovers a lead to the serial killer, a reporter's questions force Aceveda to explain problems he thought were buried fair in the past, while Vic assists Connie as she tries to quit crack cold-turkey in a desperate attempt to keep her son, leaving the other Strike Team members to investigate a strip-club mugging ring on their own.

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.

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.

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.