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.

John copes with the aftermath of his kidnapping. Sammy closes in on the real robbers. Lydia continues to pursue John’s kidnappers and becomes more intimate with Russell.

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.

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.

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.

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.

It's the last day on patrol for Tang, as she prepares to move to another precinct as sergeant. But first she wants to tie up some loose ends on the beat. Lydia is pressured to make a decision about the extent of her police duties during the rest of her pregnancy. With Sammy recovering from injuries, Ben and Dewey are partnered together. But Ben is bent on tracking down the prostitute he's been trying to help and then getting her and her daughter away from the abusive pimp controlling their lives.

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.

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.

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.

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.

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.

An investigation is opened after Ben, John, and Officer Chickie Brown encounter an infant crawling down the street. Lydia takes a personal interest in the case after Child Protective Services gets involved, and goes out on a limb for the mother. Meanwhile, Sammy and Nate are furious when they learn their teenage eyewitness won't get police protection due to lack of funds, and put up their own money after an attempt is made on her life.

In an effort to recover Detective Daniel "Sal" Salinger's stolen weapon, Sammy and Nate crack down on the residents in the neighborhood where it occurred. Elsewhere, a man exposes himself to Lydia.

A young Jane Doe found murdered in an alley sets Lydia on an emotional journey, and she discovers her suspect was involved in a cold case. Meanwhile, Sammy's wife, Tammi, decides to embark on a new career, and Nate deals with some family issues and reveals a deep secret.

Lydia and her partner, Detective Russell Clarke, investigate a string of jewelry thefts in Bel Air and Ben discovers one of the victims is someone he knows. In another matter, Ben must face his past when it comes back to haunt him. Meanwhile, John reveals a secret he's been harboring for a long time, Russell has troubles at home, and Sammy and Nate take extraordinary steps to protect their eyewitness, Janilla, after another attempt is made on her life.

Officer John Cooper clashes with his new boot, Gary Steele, a vet from Afghanistan. Lydia struggles to balance detective work and motherhood. Ben Sherman falls in with a sketchy crowd of cops, while Sammy Bryant is trapped in a hellish custody battle with Tammi.

Ben and John are called to the home of a man who wants them to find his dog, and another in which a drug overdose led to homicide. Chickie and her partner, Officer Bill "Dewey" Dudek, butt heads after he makes some poor decisions that may have repercussions, and later, Dewey finds himself in an embarrassing situation.

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.

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.

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.

A breakdown in the LAPD's dispatch system makes a difficult job even harder for the cops, all of whom are already grappling with communication issues. Lydia, in a moment of weakness, reaches out to her old flame, Terrell. John is assigned a new partner; Ben and Sammy's partnership is strained just as Ben makes a romantic connection on the job.

On his first day, rookie officer Ben Sherman is assigned to veteran cop John Cooper, his no-nonsense training officer. After being involved in a fatal shooting, Ben already begins questioning his career choice. Detectives Sammy Bryant and Nate Moretta try to convince a young teen to testify after learning she is an eyewitness in the attempted murder of a boy who was mistaken for a gang member. Meanwhile, Detective Lydia Adams investigates the disappearance of a young girl.

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.

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.