The officers try to deal with the difficult consequences of a plotted attack on the city of Los Angeles.
Nolan teams up with new detective Nick Armstrong on a case that reopens the pages of the past.
Officer Nolan takes his relationship with Jessica to the next level. Meanwhile, he tracks a difficult case with a homeland security agent involved.
Officer Nolan's first day in new training gets off to a bad start.
The rookies embark on new developments, and Chen's mother comes to stay with her, which causes some problems to Chen.
Los Angeles is suffused with chaos and danger due to an approaching missile attack.
John and Jessica's relationship faces some new challenges after some important news are revealed.
It's Nolan's birthday, yet he has to keep watch on a crime scene at a law firm.
Nolan's loyalty is about to be scrutinized, and Harper reconnects with her daughter.
Officer Nolan and his team are tasked with escorting a highly dangerous serial killer to find the remains of her victims.
Nolan and the whole team start a search to rescue Officer Chen after she has been kidnapped.
Nolan takes his son's fiancée on a trip, whereas Jackson faces some troubles at work because of his relationship.
After learning some surprising news, Nolan invites Grace to a meal in his new kitchen.
Officers Nolan and Harper have to solve a murder that may be linked to national security.
Grey faces a tough situation, when he has to testify on the case of the man who killed his partner.
Officer Chen has to face Ryan Seacrest, after they respond to a call at the Los Angeles auditions of "American Idol".
Things go south, after Nolan's informant, Bianca gives him a tip regarding a shipment for Ripper.
Things spiral out of control, after Officers Nolan and Harper go on a mission to escort four juvenile delinquents to a correctional facility.
Nolan and Chen prepare for a fateful mission, while the team discovers many disturbing facts.
Nolan delves into his shocking discoveries, while his life becomes in grave danger.