Officer John Cooper returns to duty after recovering 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 Ruben Robinson, can't seem to escape helping a former CI who won't stay in safety. Ben, Sammy and Dewey chase an armed man into an elementary school, while Ben bumps heads with an intense street cop whose cynical attitude is affecting their work.

As a new, no-nonsense captain takes over, Ben has a moment of weakness during an especially trying shift, while Lydia and her new partner suspect that a convenience store homicide was a revenge murder.

It's Hood Day on the streets of Los Angeles, and Captain Rucker has the department playing hall monitors. Sammy lets old grudges die hard when he leaves a gang territory unattended, only to have a violent gang war erupt throughout the city. Ben's recent mistake continues to haunt him publicly everywhere he goes. Ruben practices his speech for his daughter's quinceañera in the midst of a murder investigation. Cooper and Tang investigate a robbery in a strict Orthodox Jewish home, leading Tang to reveal parts of her past.

Lydia finds out she's pregnant as she tracks down a 15 year old female killer, Sammy tries to come to the rescue of a dog that he accidentally shot, and Tang and Cooper try to help a homeless Marine.

John has an eventful shift on the day he receives his pin for 20 years of service, Sammy and Ben try to out-prank each other, and Lydia and Reuben suspect that a father may have killed his 30 year old son.

A documentary film crew accompanies Cooper and Tang on their shift, Ben suspects that Sammy may have planted evidence to help settle a score, and Lydia risks her pregnancy and takes a shift in the field.

Tang is involved in an accidental shooting on the day she is served with divorce papers, Sammy gives Ben the cold shoulder after his accusations, and Adams and Robinson investigate the death of a drug dealer.

Sherman tries to come to the rescue of a prostitute and her daughter who is also turning tricks, Cooper and Tang get a case that closely resembles Tang's shooting, and Adams and Robinson investigate the death of a pregnant nanny.

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 spends his shift trying to settle a personal score with a pimp, Tang has her last shift with Cooper before taking her promotion, and Lydia has a traumatic case on the day that she announces her pregnancy.