The team is tasked with community policing while hunting for a local vigilante; Celina's instincts are tested; Tim and Lucy discover secrets about the two new rookies.
Ahead of Bailey's return home, John looks for clues to locate Jason Wyler; Tim and Lucy swap rookies; a friendly face resurfaces at the station; Wesley feels unsettled over Angela.
The officers grapple with the aftermath of a plotted attack on the city of Los Angeles, leaving Bradford fighting for his life.
Nolan teams up with new night detective Pablo Armstrong for a murder investigation case that results in an unexpected reunion with a former love interest.
Officer Nolan navigates his relationship with Jessica and a developing rapport with Grace while working a high-stakes criminal case involving an undercover homeland security agent; Officer Chen meddles with Officer Bradford's love life.
Officer Nolan gets off to a rocky start after being introduced to his new training officer; Officer Bradford struggles to think of an appropriate birthday gift for Rachel; Officer Lopez finds herself navigating a case that triggers a personal memory.
A large sum of money used in a drug bust goes missing; the rookies become the prime suspects, as they had previously discussed what they would do with the money.
When a prison bus crashes, some inmates face severe injuries while others seek an opportunity to flee; in the wake of the accident, officer Nolan tries to impress an FBI hostage negotiator while tracking down an escaped convict.
Officer Nolan gets a lesson in respect after his arrest of a gang member leads to a free-for-all on his life; officer Chen and Bradford pull over Mario Lopez, who thinks he can talk his way out of a traffic violation.
A massive earthquake rocks the city and throws everything into chaos; Russo recommends Officer Nolan for a protective detail of Brad Hayes, a man whose dealings have put a target on his head.
When a cop is arrested by Internal Affairs for lying on the witness stand, it leads to the release of three felons whose cases he worked on; Officer Nolan finds out he is being sued by a man who claims he used excessive force which led to an injury.
Sgt. Gray informs the rookies that they must track down a specific set of crimes in a 48-hour period to qualify for their final exam; Nolan and Bishop answer a silent alarm call at will.i.am's house.
As the rookies prepare for a big exam to see who moves on to the next stage of training, Nolan and Bishop are called to the scene of a murder and learn that the victim may be tied to a potential terrorist attack on the city of Los Angeles.