'Castle' Sneak Peek: Slaughter Is Back!

Keep it cool, Castle. Looks like an old friend is paying our favorite TV mystery writer turned private investigator a visit. And by “old friend” we mean a guy who almost got him killed six times.

In this sneak peek clip from the upcoming Castle episode “Cool Boys,” Richard Castle (Nathan Fillion) gets a visit from Detective Ethan Slaughter (guest star Adam Baldwin), who wants to pick his old pal’s brain for a high-stakes case. Yep, Slaughter is back, but Castle is not exactly happy to see him.

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It’s been years since these two polar opposites have worked together. Longtime Castle fans will remember Det. Slaughter from the Season 4 episode “Headhunters,” when he showed Castle the grittier side of police work. We’re not sure what this caveman-like cop wants now, but considering how many times he put Castle in the line of fire in the past, all we can think is: With friends like these, who needs enemies?

Castle airs Mondays at 10 p.m. on ABC.