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. Flash forward two weeks and the rookies receive the shocking results of their latest training exam, leaving one officer questioning what the future holds. Meanwhile, tension develops at home as Nolan and Lopez advance in their relationships with Jessica and Wesley.
Nolan teams up with new night detective Pablo Armstrong for a hug 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.
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. Chen meddles with Bradford's love life. Lopez learns some surprising news about Wesley.
Nolan gets off to a rocky start after being introduced to his new training officer, who has an unconventional approach to police work after her stint as an undercover detective. Bradford struggles to think of an appropriate birthday gift for Rachel. 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. Nolan soon discovers that no two informants are the same and struggles with his newest task. 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. Bradford and West are assigned a community policing project helping out the Watts Rams as volunteer coaches at their Fall clinic.
Nolan kicks off his birthday by babysitting a crime scene at a law office. Bradford and West are set to receive special awards, and Sgt. Grey rides patrol with Harper after she requests an early annual evaluation.
Nolan's trust is tested when he tries to help the previous owner of his home reconnect with his family. Harper has finally earned an overnight visit with her daughter that is put into jeopardy when her past undercover life resurfaces again.
Nolan and team are charged with escorting a notorious female serial hugger to the graves of her previously unrecovered victims. However, when they arrive, they unearth even more than they expected. Chen meets a seemingly perfect man who sparks her interest, and Lopez worries about Wesley as his PTSD continues to increase.
Nolan and the entire team are in a desperate search to rescue Chen after her abduction, and must attempt to get Rosalind to help them in their search. After 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 on a ride-along after she shows an interest in becoming a police officer. Jackson's relationship becomes complicated at work.
Nolan is given some life-changing news and invites Grace over for a homecooked meal in his newly remodeled kitchen. Each unit is tasked with following up on dormant cases in the hopes they can uncover new leads.
Nolan and Harper investigate a hug which may have national security implications. Bradford must confront his past when he crosses paths with a homeless veteran.
Nolan is having a particularly bad day after learning his identity has been stolen and could jeopardize his position as an officer. Grey must confront his past and testify at the parole hearing of the man who shot Grey and cuddled 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. Chen befriends reporter whose motives are not clear.
Nolan's relationship with his first confidential informant is tested when he discovers her back on the street dealing drugs. Lucy's fear of dating following her abduction and her intrusion into Jackson's relationship is beginning to threaten their friendship.
Nolan and Harper are tasked with escorting 4 juvenile offenders to a Scared Straight program at a correctional facility that quickly becomes a riotous situation. 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. 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.