Castle

Season 4 Episode 21

Title: Headhunters
Air Date: April 16, 2012 at 10:00 PM PDT

With tensions rising between Castle and Beckett, Castle finds himself a new partner — Detective Ethan Slaughter (guest star Adam Baldwin, Firefly), a tough and colorful cop from the city's gang unit. But Castle gets more than he bargained for when Slaughter shows him a grittier side of police work that puts Castle in the line of fire like never before.

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