Chaos prevails in the city of angels when Cooper and Lucero are kidnapped and held hostage by a pair of tweakers. All of our cops join the frantic search to find their brothers in blue before it is too late. Sammy searches for Strokeface. Ben tries to throw Sammy off the trail while simultaneously dealing with an increasingly irrational Brooke.

Ben learns the hard way, some valuable lessons about the importance of following established procedure and protocol, Lydia's current murder investigation takes an unexpected turn, and Nate and Sammy are unprepared when a group of people they encounter turns into a violent mob.

After two men murder a man in a crowded nightclub, Nate discovers his daughter was an eyewitness. Meanwhile, tensions rise between Sal and Gil on the gang task force, and Sammy confronts his wife, Tammi, after discovering she has been photographing gang members.

On Ben's final day as a rookie, he decides to force John to get the surgery he needs to relieve his back pain which, in turn, will end his need for painkillers. Meanwhile, Josie discovers that her son is the man Lydia has been seeing. Elsewhere, Sammy decides to go back to regular patrol.

Ben, assigned to work on his own for the first time, responds to a call about a 9-year old girl who wandered off and finds himself emotionally distraught over a woman who is being harassed by an ex-lover with a tendency towards violence against women. Lydia and Rene spend the day checking assisting Brianna, the mother of the baby found crawling down the street. Over in Gangs, Detective Gil Puente leads the task force to take down ex-banger Trinny Day, but clashes with Sal and Sammy who find him loud and abrasive. When Chickie is assigned to ride with John for the day, he discovers she has no "command presence" and has lost her edge, suggesting it may be time for her to get out of police work.

John, Ben, and Chickie are sent out as part of a maximum deployment to capture the “Canyon Rapist,” a perp who's been impersonating a cop. Russell is back, but on light duty as he continues to struggle with his recovery after being shot. While working a double-homicide with his old partner, Lydia, he discovers he's no longer up for the job. Sal plans a special night out to commemorate his wife's promotion, but their evening is ruined when their daughter reveals Sal’s affair with TV news reporter Mia Sanchez. Chickie gets a chance to prove to herself -- and others -- that she still has what it takes to be a good cop.

On Hood Day, a day where gangs seek retribution, LAPD is trying to keep the peace by camping out in neighborhoods prone to violence. Sammy and Ben leave their assigned neighborhood with disastrous results. Meanwhile, the neighborhood grabs a golden opportunity to seek a little retribution of their own against the gang banger who has been terrorizing them. Elsewhere, John and Jessica discover that another group of neighbors will go to any lengths to get a registered sex offender off their streets.

The funeral of a major drug dealer brings gangsters of all kinds out of the woodwork, there is chaos in the streets but as our cops learn sometimes the greatest threats come from within. Lydia and Ruben investigate the drug related murder of Sgt. Hill’s son; they discover police corruption in the process and clash over how to handle it. Ben suspects that Sammy did not destroy the tape and decides to take matters into his own hands with tragic consequences. John sinks farther into his loneliness.

When Sammy discovers Marta has made bail, and fearing another attempt will be made on Janilla's life, he arranges to have her stay with Lydia, but Janilla's safety is compromised after she visits her old neighborhood. Meanwhile, Sal continues to spy on his daughter's activities, Dewey flips out when Chickie confronts him about his drinking problem, and Russell is caught in the middle when he attempts to defuse an ongoing domestic battle between a neighbor and his wife.

Jessica goes the extra mile to assist a homeless war vet obtain an ID so he can be admitted into a shelter . Meanwhile, Sammy is determined to save a dog after he accidentally shoots it in the leg. Elsewhere, Lydia struggles with a serious personal matter while she and Ruben investigate the murder of a man who sheltered and aided women in need.

Ben finds himself heading down a slippery slope as he attempts to help the daughter of a prostitute, putting him in hot water with the woman's pimp. Lydia and Ruben investigate the murder of a gang-banger who may have been killed over a graffiti tag. Tang faces more questions about her shooting of an innocent bystander, which could determine whether she gets promoted to sergeant.

John and Ben are the first responders to a gruesome triple homicide in Hancock Park, where a mother is bludgeoned to death and her young daughters are found bound, gagged, raped and dead in their bedrooms. In investigating the case, Lydia and Rene realize they have two very different investigation styles. Meanwhile, Sammy continues to have problems with his wife and Ben confronts John about his increasing reliance on pain pills.

Lydia and Rene are called to Compton to investigate the murder of a young SULA student, only to discover that the girl was not exactly who her parents claimed she was. Meanwhile, John takes Ben with him to Indian Wells to attend the funeral of his friend, a cop who committed suicide. On the way back, they stop at the rehab center to check in on Dewey.

Lydia and Josie are assigned to assist Sammy and Nate with a series of gang murders. John discovers he can't stand the "new and improved" Dewey, fresh from rehab, when he's forced to ride with him in order to evaluate whether Dewey is competent to return to duty. Ben must then ride with Chickie, who drives him nuts with her very personal questions about his private life and his new relationship with the "cop groupie" he's been seeing.

Ben has a confrontation with his mother’s rapist after the man is released from prison and is devastated when his mom reveals some information she's been keeping secret for years. Meanwhile, Lydia and Josie continue to bump heads, and Sammy deals with his wife’s betrayal.

When crime scene photos from the case of the celebrity suspected of murdering his estranged wife show up on the internet, all of the first responders are suspended, including Lydia and Josie. Further investigation proves the photos were the unauthorized pictures taken by Lydia using her phone, and she's shocked when she learns who was responsible for the leak. Meanwhile, Sammy fails to pick the right guy from the line-up for Nate's murderer, and Dewey and Chickie are involved in a high-speed chase that ends in disaster.

Sammy seeks answers in the desert, Lydia and Josie babysit an important alcoholic witness before a murder trial, and John and Ben go against procedure to help a child in need.

John returns to duty after recuperating from back surgery and meets his new partner, Officer Jessica Tang, a tough and disciplined cop with her own set of baggage from working the streets. Lydia, whose new partner is Detective Ruben Robinson, can't seem to escape helping a former CI who seems unable to stay out of danger, Ben, Sammy and Dewey chase an armed man into an elementary school, and Ben bumps heads with an intense street cop whose cynical attitude is affecting their work.

John tries to save a suicidal teen in a situation that hits extremely close to home, and Sammy convinces a former addict to be an informant, with devastating consequences. Meanwhile, Jessica gets a visit from someone from her past, and Lydia and Ruben investigate a home invasion that appears to have been staged to cover up a murder.

Lydia dons a uniform and hits the streets when the shift is short a supervisor and she must fill in. Meanwhile, John and Jessica are stuck with a film crew tagging along on their calls. Elsewhere, Ben infuriates Sammy when he implies Sammy planted evidence.

Jessica and John exchange angry words after she lies to Internal Affairs about the facts surrounding her shooting of a teen with a toy. Meanwhile, Sammy continues to hold a grudge with Ben and Lydia continues to dodge questions about her condition.

John takes drastic measures to try to save Hicks while being confronted with demons from his past. Sammy’s lie about the tape weighs heavily on his conscious. Lydia and Ruben track down a John Doe. Ben’s relationship with Elena becomes more serious.

Lydia and her new partner, Detective Rene Cordero, investigate the disappearance of an elderly man. Meanwhile, Nate and Sammy investigate a freeway shooting and inadvertently threaten the integrity of a major undercover operation. Elsewhere, Chickie finds herself in the middle of a mini-riot after her new partner panics and takes a shot at a 13-year-old boy.

Lydia endures a stressful adjustment period with her new partner, Detective Josie Ochoa, as they investigate the disappearance of an illegal immigrant. Meanwhile, Russell must learn to adapt to a new desk job, Sammy and Nate look for the killer of two gangbangers, Ben catches the eye of an attractive woman, and John struggles with increasing back pain.

When a rape victim hires a lawyer and refuses to talk with the two detectives unless her lawyer is present, Lydia and Josie want to know why. Meanwhile, John strikes up an unlikely friendship with a boy who returned home after a sleepover, only to discover his parents had packed up and moved during the night, abandoning him and leaving him to fend for himself, Later on, John begins to feel the stress over the prospect of testifying at his father's upcoming parole board hearing, but he doesn't realize his testifying will open up an emotional can of worms that he's not prepared for.