Gang detective Sammy Bryant decides to ensure the safety of a key witness (Carla Jeffery) in a gangland trial by taking her to his home.
Detective Lydia Adams has to adjust to life with a new partner, Rene Cordero (Amaury Nolasco), as they investigate the kidnapping of an elderly man, while Detective Russell Clarke is hospitalized.
Chickie Brown ends up in a mini-riot when her new partner, Officer "Slug" Ferguson, accidentally shoots at an unarmed joyriding suspect.
And back at the station, everyone gathers for a retirement party for Officer Dewey.
Meanwhile, both Detectives Sammy Bryant and "Sal" Salinger struggle with their marriages.
One of the witnesses, a teenage girl named Janila (Carla Jeffery), seems unafraid to aid in their investigation, even though her cooperation might prove dangerous.
Her information leads to a raid by Sherman and Cooper, alongside Officer Bill "Dewey" Dudek (C.
Meanwhile, Sammy convinces Lydia to take in Janila in order to ensure her safety.
Sal becomes increasingly frustrated with his growing rift with his teenage daughter Kimmy (Annamarie Kenoyer).
Lydia and her new partner, Ray Suarez (Clifton Collins, Jr.), arrive in South Central, where a young SULA student/track star was murdered. Ben and John visit Dewey in rehab and attend a former police officer's funeral in Indian Wells. Officers Cooper, Sherman and Brown are dispatched as part of a maximum deployment to catch a rapist who is impersonating a police officer. Clarke returns as Lydia's partner to investigate a double homicide. Salinger's wife, Captain Susan Salinger (Denise Crosby), learns of his affair with television reporter Mia Sanchez (Lisa Vidal) through his daughter.
Two gangbangers are killed when gangsters open fire in a crowded night club and the shootings are connected to Moretta's daughter. Lydia adjusts to having yet another new partner, Det.