Beckett’s former training partner, Mike Royce, is found murdered in an alley. Clues send Beckett and Castle to LA to investigate what happened.

They find that Royce had been helping a girl who had gotten herself caught up in some serious crime activity. Twists and turns lead to a Russell Ganz, who was using the girl to help in the theft of disintegrating bullets. Ganz along with his accomplices had stolen the bullets to sell for a big payday. 

Beckett, Castle, and help from the LA police hunt down Ganz and arrest him after Kate shoots him in the leg. She let’s him know that Royce was her friend before they lock him up.

Royce had a letter for Beckett when he died, letting her know that what she has with Castle is real. The couple shares some tension filled moments in their hotel room before heading back to NYC.