Castle: What Happens When Detective Ryan's "Worst Nightmare" Comes True?

The case on Monday's Castle (10/9c, ABC) hits a little too close to home. That's especially true for Detective Ryan ( Seamus Dever ), who last season lost his badge and service weapon to the 3XK serial killer. Now, the missing gun has turned up — as the weapon that murdered the team's most recent victim. "It's a very emotional episode for Detective Ryan," creator and executive producer Andrew W. Marlowe tells "If you're a cop and you've lost your gun to somebody, and then it's used in a murder, the case becomes deeply, deeply personal to you.  It's every cop's worst nightmare...

Castle Episode Teaser: The Return of 3XK?

On next week's new episode of Castle , a crime scene looks to be the work of the mob. How does Castle know? There's concrete evidence! Eh? Eh? It this thing on?!? The case on "Kick the Ballistics" actually takes an eerie turn when the gun used in the killing turns out to be the same service weapon of Detectice Ryan's that was stolen by the serial killer, 3XK. What will that mean? Tune in, find out, read our review of the most recent episode and then take a look ahead below: