Castle tries to catch up with Beckett about what he’s found in LA but Martha interrupts and Beckett runs as not to get caught and keep the faux separation going. Later, he goes to the 12th and tells Beckett that he learned about LokSat during his disappearance and it’s connection to Bracken and chose to forget it in order to protect her from herself. She’s obviously upset and tells him she needs time to process what he’s told her.  

Martha’s book “Unsolicited Advice” is published. The dedication is to Castle, “Without your constant stumbles in life the advice in this book would not have been possible.”

Daniel Bardot, a recruit officer at the NYPD academy is murdered and the bullet is cut out of his body. Lanie is able to find a bullet fragment and links it back to a gun used at the academy but the gun is missing. Captain Beckett goes to the academy as a guest instructor to try and find the killer. 

She finds a note in Bardot’s locker threatening him if he didn’t keep his mouth shut. Turns out he thought someone in his class was dealing drugs. Beckett uses and interrogation training class to figure out that Recruit Officer Chambers is the guilty party. 

Chambers says that Bardot leveraged the info about the drugs to get $5,000 but didn’t know why he needed it. Chambers also says that Recruit Officer Rachel Decker was Bardot’s girlfriend. She tells Beckett that Bardot was going out at night and coming back smelling of fish but wouldn’t tell her where he’d been. 

Bardot stole the gun that he was shot with. He also went to a computer store known to sell black market hardware and software. They find out through street cameras that Bardot was meeting with Jack Flanagan from the Irish mob. Beckett thinks he was a mob mole in the NYPD. 

Turns out that Rachel Decker is Jack Flanagan’s daughter. She feared that she’d be booted out of the academy if anyone found out and she thinks Bardot tried to help her and got himself killed. Beckett asked Rachel to wear a wire and try to take down her estranged father. Rachel holds a gun on him and he swears he didn’t kill Bardot. 

Flanagan says he saw a car the night Bardot was killed. Espo and Ryan find camera footage and get a license plate that traces back to Sgt. Ortiz’s vehicle from Academy motor pool. When Beckett confronts him he says he hadn’t used that car in days. 

The killer is Deputy Commissioner Malone because Bardot hacked his computer and realized that Malone was stealing money. Beckett takes down Malone and saves Ortiz. 

Later, Castle tells Beckett that he won’t remain on the sidelines any longer. He’s as invested in LokSat as she is. She agrees that they will take them down together.