Danger is ever-present as the officers of the Mid-Wilshire precinct grapple with the aftermath of a plotted attack on the city of Los Angeles, leaving Officer Bradford fighting for his life.

Nolan teams up with new night detective Nick Armstrong for a murder investigation case that results in an unexpected reunion with a former love interest. Officer Bradford reluctantly accepts help from Officer Chen as he prepares for his sergeant exam, and Officer West pursues an unconventional move after finding himself in need of a new home.

Officer Nolan navigates building tension in his relationship with Jessica and a developing rapport with Grace while working a high-stakes criminal case involving an undercover homeland security agent. Meanwhile, Officer Chen meddles with Officer Bradford’s love life, and Officer Lopez learns some surprising news about Wesley.

Officer Nolan gets off to a rocky start after being introduced to his new training officer, Nyla Harper, who has an unconventional approach to police work after her stint as an undercover detective. Meanwhile, Officer Bradford struggles to think of an appropriate birthday gift for Rachel, and Officer Lopez finds herself navigating a case that triggers a personal memory.

As part of their second phase of training, the rookies are asked to develop their first confidential informants. Officer Nolan soon discovers that no two informants are the same and struggles with his newest task. Meanwhile, Officer Chen’s mother complicates her home life when she comes to stay with her.

An emergency alert of an impending missile attack sends Los Angeles into chaos and uncertainty, while the officers each try to keep the peace and deal with their own disasters.

John and Jessica’s relationship gets a lot more complicated after she delivers some surprising news. Meanwhile, Officer Bradford and Office West are assigned a community policing project helping out the Watts Rams as volunteer coaches at their fall clinic, along with Rams players Eric Weddle and Robert Woods.

Officer Nolan kicks off his birthday by babysitting a crime scene at a law office. Meanwhile, Officer Bradford and Officer West are set to receive special awards, and Sgt. Grey rides patrol with Officer Harper after she requests an early annual evaluation.

Officer Nolan’s trust is tested when he tries to help the previous owner of his home reconnect with his family. Meanwhile, Officer Harper has finally earned an overnight visit with her daughter that is put into jeopardy when her past undercover life resurfaces again.

Officer Nolan and team are charged with escorting a notorious female serial killer to the graves of her previously unrecovered victims. However, when they arrive, they unearth even more than they expected. Meanwhile, Officer Chen meets a seemingly perfect man who sparks her interest, and Officer Lopez worries about Wesley as his PTSD continues to increase.

Officer Nolan and the entire team are in a desperate search to rescue Officer Chen after her abduction and must attempt to get Rosalind to help them in their search. Meanwhile, after Officer Lopez discovers Wesley unconscious from a dangerous cocktail of alcohol and pills, she is forced to keep him close by.

Nolan takes his son’s fiancé, Abigail, on a ride-along after she shows interest in becoming a police officer. Meanwhile, Jackson’s relationship is becoming complicated at work.

Nolan is given some life-changing news and invites Grace over for a homecooked meal in his newly remodeled kitchen. Meanwhile, each unit is tasked with following up on dormant cases in the hopes they can uncover new leads.

Officers Nolan and Harper investigate a murder which may have national security implications, while Officer Bradford must confront his past when he crosses paths with a homeless veteran.

Officer Nolan is having a particularly bad day after learning his identity has been stolen and could jeopardize his position as an officer. Meanwhile, Sgt. Grey must confront his past and testify at the parole hearing of the man who shot Grey and murdered his partner.

Officers Chen and Bradford respond to a call at the Los Angeles auditions of “American Idol,” and Officer Chen ends up facing Ryan Seacrest and the judges. Meanwhile, Chen befriends a reporter whose motives are not clear.

Officer Nolan’s relationship with his first confidential informant is tested when he discovers her back on the street dealing drugs. Meanwhile, Lucy’s fear of dating following her abduction and her intrusion into Jackson’s relationship is beginning to threaten their friendship.

Officers Nolan and Harper are tasked with escorting four juvenile offenders to a Scared Straight program at a correctional facility that quickly becomes a riotous situation. Meanwhile, Nolan is uncertain about his relationship with Grace after she fails to introduce him to her ex-husband.

Their rookie year is coming to an end and officers Nolan, Chen and West are about to be squeezed harder than ever before as their training officers evaluate whether they are truly ready for the job. Meanwhile, after one of their rookie classmates is involved in a shooting, the team uncovers some unsettling evidence .

Nolan's discovery goes much deeper than he expected and could put his life and career in jeopardy.

Nearing the end of his training, Nolan now faces his biggest challenge as a police officer yet when he must come to terms with the choices he has made in pursuit of the truth.

Officer John Nolan and Officer Nyla Harper are assigned to a community policing center to help rebuild their station’s reputation in the community. Nolan is determined to make a positive impact but Nyla has her doubts.

Officer John Nolan's mom makes an unannounced visit that complicates his life, and Sergeant Grey considers retiring.

Officer Jackson West’s relationship with his new training officer, Stanton, has escalated and he begins to work with Sergeant Grey to find a solution.

Officer Nolan is taken hostage by a man with nothing to lose while the station goes on lockdown and races to identify the suspect before time runs out. Meanwhile, Officer Jackson and his training officer, Officer Doug Stanton, reach a tipping point in their relationship that could end Jackson’s career.

Officer Nolan’s decision to return to school in order to become a training officer is proving to be much harder than he expected. Meanwhile, Officer Chen considers going into undercover work after getting a taste of the job when Harper’s former colleague needs help.

The team gets the true crime docuseries treatment when they analyze a recent case featuring a former child actor whose adult life has garnered him a cult following.

Officer Nolan, Officer Harper and Detective Lopez are assigned to the kidnapping of the son of a criminal court judge who has a long list of enemies who could possibly be involved.

An Amber Alert sends the team on a race against time to find a newborn infant who was stolen from a local hospital. Meanwhile, Officers Jackson and Chen work their last shift as rookies as Officer Nolan continues on for 30 more days.

Harper and Nolan respond to a bank robbery in progress and realize the motives of the thief run much deeper than just needing money. Jackson and Chen’s first day riding without training officers isn’t what they thought it would be.

When professor Fiona Ryan’s car window is smashed following a series of mysterious notes, Nolan volunteers to guard her house overnight. Lucy notices that Tim is being much nicer to his new boot than he was with her and she does not like it.

After rushing his son, Henry, to the hospital following his collapse, Nolan is reunited with his ex-wife, Sarah, and they must come together to help their son. Meanwhile, Detective Lopez discovers “La Fiera” is in the same hospital and wants to find out exactly why.

Officers Nolan and Bradford hope they can de-escalate a drug war before any innocent lives are lost. Meanwhile, Officer Harper hopes she can get Officer Chen ready to go undercover.

Officer Nolan mildly injures himself while chasing down a shoplifter and the local DA wants to charge the suspect with assault despite Nolan's wishes. Meanwhile, Lucy goes undercover, Lopez' wedding venue is seized by the FBI and Nolan meets his new neighbor.