A massive earthquake rocks the city and throws everyone’s patrols and its citizens into chaos. Meanwhile, agent Russo recommends Officer Nolan for a protective detail of Brad Hayes, a man whose dealings have put a target on his head.

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 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.

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.

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 is once again face-to-face with serial killer Rosalind, and she wants him to know she's not done with him yet. Meanwhile, officers Bradford and Chen work undercover with Detective Lopez and the Las Vegas Police Department to arrest leaders of a major criminal enterprise.

Officer John Nolan is moving closer to his new role as a training officer. In preparation, he is tasked with overseeing Officer Aaron Thorson and must uncover the truth about another officer’s suicide. Meanwhile, Lucy’s successful undercover assignment earns her an invitation for specialized training in Sacramento and she must decide if this is the path she wants to take.

Officer John Nolan and a sleep-deprived Celina investigate a cash deposit linked to an old DEA case. Meanwhile, Wesley grows increasingly concerned about his deposition and is shocked when he realizes Elijah’s attorney is a familiar face from his past.

Following their time as foster parents, Bailey has decided she wants to have a baby and forces John to reconsider their decision to not have children. Meanwhile, John and Celina discover a prison escapee whom they fear is out for revenge and race to find her before it is too late.