It’s the rookies one year anniversary of their training program and the start of the 30-day push by their training officers. In a month, they’ll be on their own. 

Lucy is dating Emmitt, the EMT. 

Lopez says her mother and mother-in-law are hijaking her wedding while she’s focusing on her detective’s exam. 

Nolan mentions that he’s never worked such a slow day, which Harper points out has jinxed them. 

Officer Chris Rio, a fellow rookie and Jackson’s friend and main competitor for top of their class, is in pursuit of an armed man in a grey Maserati for a shots fired called. Bradford thinks Rios sounds too amped up over the radio. The other officers join in the pursuit. When the Maserati crashes into another car, Chris rushes in and ends up getting shot. The Maserati takes off once again. 

Harper and Nolan find the car on a parking deck. The driver is gone but the gun is still inside. Harper tells Nolan to stay with the gun, photograph it and bag it while she goes after the shooter.

The get an ID on the driver of the Maserati. It’s Serj Darien a member of the Armenian mob. He isn’t at his home but they find police files leading Bradford to believe that a dirty cop is giving intel to the mob. 

Grey makes Lopez an active detective on the case because he says he knows he can trust her. She’s already passed the exam and they’re short-handed.  

Nick encourages Harper to take his unmarked car to get to her custody hearing and he rides with Nolan. He watches as Nolan puts all of the evidence in a lock box in the back of his shop.

Nick attaches them to Lopez’s call to execute the search warrant of Ruben Darien’s home. Nolan runs into Officer Erin Cole who was involved with Chris Rios. Chris is in surgery at the hospital. Back at the precinct, Nolan goes to check in the evidence from the Maserati and the gun is missing. 

Officer Chris Rios dies, making the missing gun the weapon in a police officer’s murder. As the key for the vehicle lockboxes is universal and the box wasn’t broken into, they conclude that a cop must have taken the gun. Even if they can get the gun back, the chain of custody has been broken and it can’t be used as evidence in the case. 

Officer Erin Cole had her body cam turned off. She ends up on the run when the LAPD go to question her. She turns the gun on herself when Nolan finds her but he convinces her to testify to help take down the mob and avenge Chris. She says “Armstrong” as Det. Armstrong comes up behind her and shoots her, believing she was going to shoot Nolan.

Later, Nolan rewatches his own body cam footage and realizes that Cole said Armstrong’s name before she actually saw him. That night, Nick Armstrong meets with Ruben Darien who says he did a good job.