Beckett fields a call from a man who says he’s a “big fan” and claims to have committed a murder. The body of Alex Peterman, a personal injury attorney, is found at Grand Central Station. The five bullets dug out of his body are etched with letters that spell “Nikki.” Believe it or not, this murder has been dedicated to Nikki Heat.

The killer calls again, addressing Beckett as Castle’s favorite fictional character. He’s claimed another victim. Four slugs pulled from a woman found dead at the Central Park Carousel are marked with letters that spell “will.” It’s a message: “Nikki will…” FBI Agent Jordan Shaw (guest star Dana Delany) and her entourage of Special Agents swarm the scene. This is their case now.

The second victim is Michelle Lewis, a dog walker. The FBI builds a high-tech war room at the precinct where various smart boards and computers are set up. Castle loves all the cool gadgets. He’s also a big fan of Agent Shaw. Beckett is seething. We’re not sure if it’s because Shaw is invading her territory with the case, or if it’s because she’s invading her territory regarding Castle. What do you think?

A print on Michelle Lewis’s purse matches the pinky of a paroled man named Donald Salt. His partial print was also found at Grand Central Station. Coincidence? No way. Shaw forces Castle to stay in the car during the arrest. But when Salt spots the feds and bolts, Castle takes him down with a Taser he’d been playing with in Shaw’s vehicle.

As Beckett cuffs Salt, she notices his hand is bandaged and his pinky finger is missing. Salt sold his finger online to the killer, who used the displaced digit to trick the cops. Beckett notices a series of numbers written on Salt’s bandage. The killer left a code.