Russell's replacement investigates a possible abduction with Lydia, while Nate & Sammy check out a shooting that's part of an undercover operation.

While investigating a triple homicide, Lydia and Rene realize they have very different styles of detective work; And Ben confronts John about his reliance on pain pills.

Ben winds up in a patrol unit alone for the first time. Among the cases he has to handle on his own are a missing girl and a suspected stalking case

Lydia and her new partner, Ray Suarez, arrive in Compton, where a young USC student was murdered

After gangsters open fire in a crowded club, tensions rise between Sal and Gil on the gang task force. And Sammy confronts his wife about crossing the line too often.

The Southland officers are sent out to capture a rapist impersonating a cop. While Lydia's reunited with her former partner, Russell, Sal's secret affair is revealed to his wife.

A group of Los Angeles police officers and detectives respond to a gangland shootout, while two homicide detectives frantically search for a missing

When officers John Cooper, Ben Sherman and Chickie Brown rescue a baby girl found alone crawling across the middle of an LA intersection, the hunt for her mother begins.

Ben reveals details of his past and why he chose to be a cop to Cooper.

When an unidentified female body turns up in an alley, Gang Detectives Sammy and Nate have their work cut out for them

When Sal's gun is stolen, Nate & Sammy launch a manhunt to retrieve the weapon, only to make a disturbing discovery, a local gang is using military weapons to become a street army.

When jewelry thieves begin robbing Bel Air homes, Officer Ben Sherman breaks police policy and becomes personally involved because he knows one of the victims.

The day takes a turn for the worse when officers John Cooper, Ben Sherman, Chickie Brown and Dewey find a member of Marta's Avenue gang dead in a trunk outside Dodger Stadium.

Officer Cooper clashes with his new "boot" -- Gary Steele, while Lydia Adams tries to balance detective work with motherhood.

After Dave Mendoza is injured in a drive-by, Ben takes is upon himself to solve the case -- much to Sammy's dismay.

A breakdown in the dispatch system makes a difficult job even harder for the cops. Lydia reaches out to her old flame and Cooper gets a new partner.

John and Lucero settle into their new friendship during a day filled with strange calls. While Ben and Sammy respond to an insane bank robbery call.

John thinks about life after the LAPD. Lydia connects with a man she sent to Death Row. And Sammy becomes a tabloid celebrity after a very public act of heroism.

The day's events bring all of our cops face to face with some of their greatest fears. The death of a baby shakes Lydia to her core.

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 conscience.

The funeral of a major drug dealer brings gangsters of all sorts out of the woodwork.

Chaos reigns in the city when Cooper and Lucero are kidnapped and held hostage by a pair of "tweakers" and our cops join the frantic search to find them... before it is too late.

John copes with the aftermath of his kidnapping, while Sammy closes in on the real robbers, Ben feels the pressure and Lydia becomes closer with Russell.

Officer Cooper gets a new partner -- Jessica Tang; and Lydia has a new partner as well -- Ruben Robinson,

Tang and Cooper are attacked on the street, while Lydia and Ruben question the unassuming grandmother of a murder suspect. The force gets a new captain.

Bearing a grudge, Sammy leaves a gang territory unattended, only to have a violent gang war erupt throughout the city.

Jessica tries to help a homeless vet get an ID so he can be admitted to the homeless shelter. Sammy's determined to save a dog after he accidentally shot it in the leg.

Cooper tries to save a suicidal teen in a situation that hits close to home, while Jessica gets a visit from someone in her past.

Sammy tries to make amends after the murder of a young man who agreed to testify in one of his cases. John and Jessica find themselves babysitting a documentary film crew.

Jessica's day goes from bad to worse in a shootout. Sammy holds a grudge against Ben for not backing him up during an arrest.

While Tang gets an update about the boy she shot, John wants her to come clean about what really happened. Ben tries to intervene in the life of a prostitute, but makes things worse.

Ben heads down a slippery slope as he attempts to help the daughter of a prostitute. Tang faces more questions about shooting an innocent bystander -- which could affect her future.

Tang prepares to move on to a new precinct, but first she wants to tie up some loose ends on the beat. Lydia is pressured to make a decision about her future.

Lydia and her new partner hunt a cleaning lady's killer. John and Ben rescue an officer during a bank-robbery shootout. Nate and Sammy investigate the murder of a gang member.

Sammy and Nate feel threatened when Sal calls in Lydia and Josie to help them solve a series of gang murders.

Ben seeks revenge when his mother's rapist is released.

Sammy & Nate get into a deadly gang confrontation. Ben makes a series of rookie mistakes and Lydia works a gang homicide that leads to an unorthodox killer.

Lydia and Josie catch a complicated rape case on the Westside. John bonds with an abandoned teenager, while also having to deal with testifying at his own father's parole hearing.

While working a celebrity murder, Lydia discovers the pros and cons of being in the spotlight.

Lydia gets suspended from duty and bonds with an injured witness. A high-speed chase haunts Chickie, and John tries to clean up a neighborhood.

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.

Ben deals with John's escalating drug problem as Sammy prepares for fatherhood. Lydia embraces a teenage victim and fights her emotions during a high-octane shootout.

On Ben Sherman's final day as a rookie, challenges abound -- none more daunting than how to handle his partner's growing reliance on painkillers.