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.

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.

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.

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 .

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.

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.

When a new designer drug hits LA streets, it turns users into “zombies,” and Officer Nolan and the team have a Halloween they won’t soon forget. Back at home, Lucy questions whether her apartment building might be haunted.

The team responds to the report of a severed hand washing up on the beach and are on the hunt to find its owner. Meanwhile, Tim attempts to prove he isn’t a control freak to Lucy and invites her on a double date with him and Ashley.

Officer Harper puts Officer Aaron through “Plain Clothes Day,” but the exercise is interrupted by an unsuspected visitor. After two witnesses for an upcoming grand jury case are murdered, the team must track down the killers before it’s too late.

Officer John Nolan and the team feel they must negotiate with a distraught man who is holding a hospital hostage to ensure his wife receives a lifesaving surgery.

Sergeant Grey supports Officer Nolan’s desire to become a training officer and offers to ride with him for the day to get him ready. Meanwhile, Tim and Lucy must manage expectations in their respective relationships as they decide on their plans for Mother’s Day and a romantic vacation.

Officer John Nolan and the team investigate the unexpected death of a suspect in police custody. Their search also uncovers a very delicate loose end that could jeopardize Officer Celina Juarez's career. Meanwhile, Sergeant Grey and his wife, Luna, go to New York to visit their daughter, Dominique, only to realize she never made it home from the night before.

After one of their own is shot, the team suffers a series of close calls and realizes their division may be a target for a group of masked assailants.

In the aftermath of the assaults in the explosive season five finale, the team must now try to understand why they were targeted and if there is a bigger plan in place. Meanwhile, Nolan must survive his last shift before his wedding to Bailey.