Nathan Fillion is having a Firefly reunion on Castle. Who's showing up?

The once and future Malcolm Reynolds has never shied away from dropping little tributes to Joss Whedon's late, lamented sci-fi western in his current gig on ABC's hit cop show. But now he's going to bring more than an old costume ... he's bringing an old cast member.

Since he's no longer busy grunting at nerds, spies and nerd-spies, Adam Baldwin is going to drop by Castle and Beckett's precinct for a guest spot playing a cop named Ethan Slaughter. (Of course that's his name. I wonder if he was also a sergeant in the Marines before joining the force.)

Anyway, Slaughter is described by TV Guide as:

a rough and tumble cop from the city's gang unit who lands a case that Castle is desperate to follow. Along the way, Slaughter shows Castle a dirtier side of police work that forces Castle to reconsider what he's willing to do to close a case. As the season nears its cliffhanging conclusion, expect this new alliance to place Castle in the line of fire like never before.

I will bet a dozen donuts that, at some point during the episode, the former Jayne Cobb with say the following to the former Capt. Mal: "My days of not taking you seriously are certainly coming to a middle."

Let's just hope it's as awesome as this, my favorite time Fillion's two worlds collided:

(via TV Guide)

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