He's gonna be playing Detective Slaughter, and his name pretty much wraps it all up.

So Nathan Fillion told me at PaleyFest a few weeks ago, previewing the April 16 episode of Castle in which former Firefly pal Adam Baldwin stops by as someone who "can't be charmed" by our favorite author.

But you can bet Castle is sure gonna try, as he attempts to distance himself from Beckett and tags along with this new detective on a case involving local gangs on the upcoming "Headhunters." Check out the official ABC promo now and then click through a series of photos from it below:

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.