In "Knockdown," we learned Hal Lockwood is deeply-connected to the murder of Beckett's mom. During her weekly visit to the prison, Beckett discovers the hired assassin has been transferred to general population where he promptly kills Gary McAllister, one of three police officers who kidnapped mobsters for ransom back in the day. The other known dirty cop was the deceased John Raglan, the lead investigator in Beckett's mom's case. Someone very powerful is looking cut off all avenues of the investigation.
BOOM! A flash bomb is detonated at Lockwood's arraignment. It's chaos in the courtroom as the prisoner makes a daring escape by helicopter. Castle believes there's a third renegade cop out there who can bring down the mastermind of the kidnapping scheme. This third cop could be Lockwood's next target. The chopper is found in a hangar in Jersey. It was stolen and returned before anyone knew it was missing.
An officer named Chuck Ryker may have aided in Lockwood's escape. He's found with a bullet to the head. The payoff money Ryker received bounced through banks in Dubai. This case is much bigger than just the kidnapping of mobsters in back alleys. Beckett thinks the third cop is the one pulling all the strings. Castle realizes old arrest reports were altered in the records room years ago.
Captain Montgomery tells Ryan and Esposito that if they locate Lockwood they should take him down. He's obviously worried about Beckett's safety. Her dad is, too. That's why Jim Beckett pays a visit to Castle. He wants him to convince his daughter that her life is worth more than her mother's death.
Castle wants Beckett to walk away from the case. He urges her to think about how her dying that would affect those who love her. Her dad...Josh... Then Beckett asks, "And what about you, Rick?" This leads to an intense exchange where Castle admits that he doesn't know where he stands with her. He doesn't know what they are. Beckett clears things up for him. She says, "You know what we are, Castle. We are over." Not good.
Beckett is shocked when Captain Montgomery agrees to kick Castle to the curb. He says the only reason he kept him around this long is because he was good for her. Montgomery says they can't win this thing because there are no victories. There's only the battle. These are stirring words. Of course, we have a hard time digesting them when Lockwood shows up at Montgomery's home with a plan to kill Beckett. Believe it or not, Roy Montgomery is the third cop.
The next day, Montgomery kisses his wife and kids goodbye. He then seals some secret files into a envelope to be mailed. Montgomery also makes sure several of his handguns are fully loaded. Then the call is made to Beckett. Montgomery wants her to meet him at the hangar where they found the stolen chopper, which is exactly the plan Lockwood had laid out for him. Beckett is heading into an ambush.
Esposito and Ryan track down a retired cop who used to work in the records room. The guy was in the academy with Raglan and McAllister, but he wasn't dirty. He says the two rogue cops were tight with another rookie. His name: Roy Montgomery. Ryan and Esposito know their boss is the third cop-the one who altered the records. It's such a devastating shock that it actually has these two partners coming to blows. Ultimately, they know it's all true. They also know Beckett is in danger.
Beckett receives a text from Ryan about Montgomery just as she sees him holding an outstretched gun at the hangar. He explains that he was a rookie when the incident with Raglan and McAllister went down. He tried to make up for it by being the best cop he could be. He knows that Beckett's mom died because of actions he helped set in motion.
All these years, Montgomery was grateful that Beckett was in his command so that he could protect her. Believe it or not, he's doing so right now. That's why he won't give her the name of the mastermind. He brought her to the hangar to lure in the killers. Montgomery called Castle to take Beckett away once they arrive as he makes his last stand as a cop. BANG! BANG! BANG! A gunfight with the hired killers is a bloodbath. Lockwood is dead, as is Captain Roy Montgomery.
Beckett tells Castle, Esposito and Ryan that, as far as the world's concerned, Roy Montgomery died a hero. She speaks of his fine character at the cemetery. Everyone is captivated by her words. Everyone but Castle. He sees a flash in the distance. BANG! A gunshot rings out. Beckett's been shot! Castle cradles her in his arms. He pleads, "Don't leave me, Kate. I love you." These are the last words Beckett hears before her eyes close and we... FADE TO BLACK.