Castle S4E21 Headhunters

Castle Season 4 Episode 21 Online – 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