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.

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.

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.

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.

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.

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.

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.

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 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.

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.