This week’s episode of “Castle” (“Headhunters”), was a treat for all the Brown Coats, the extraordinarily devoted fans of Nathan Fillion’s previous show, “Firefly.” His former co-star Adam Baldwin guest starred as Detective Slaughter, a cop from the gang unit that becomes Castle’s reluctant temporary partner. Slaughter is a 1970s style detective, who is willing to bust heads and bend the rules in order to make his case. Baldwin and Fillion proved that they are just as much fun to watch on earth as they were in space. Their first scene together contained the ultimate shout out. When Castle learns that a bag of severed heads was found, he is determined to tag along on the case. Slaughter agrees — provided that Castle gives him his brown leather jacket. For the uninitiated, “Firefly” fans call themselves Browncoats after the brown dusters that the “Firefly” characters wore. Well played, “Castle.” Watch the clip above and see if you get all of the inside jokes.
Once Castle hops into Slaughter’s muscle car, he realizes this is going to be nothing like working with Beckett. Slaughter wants him to carry a gun, instead of stay safely on the sidelines, Slaughter’s first gambit is to tell a murder victim’s father that his son is dead, in the hopes that he will lead them to the perpetrators. Esposito (Jon Huertas) warns Castle that Slaughter’s last three partners died in the line of duty.Slaughter tells Castle not to call for back up when they hunt down a suspect in a bar.Castle ends up in a fight,and gets a bloody nose. But he enjoys being treated like a real cop.
Beckett (Stana Katic) is so disturbed by seeing Castle happily working with Slaughter, and being distant with her, that she discusses it with her therapist. He points out that Castle may have fallen out of love with her, or be protecting himself because she pulled away.
Castle’s infatuation with Slaughter abruptly ends when he says Alexis (Molly Quinn) has a great ass. Castle punches him. He grows even more concerned when Slaughter seemingly kills someone — which turns out to be a set up with an undercover cop. and throws a witness into a garbage truck to get him to talk.
Meanwhile, Alexis gets into every college that she applied to including Stanford. Alexis isn’t sure she wants to go to Stanford since they rejected her when she applied for early decision. It’s a parallel to the Caskett relationship. Castle seems to realize that he’s stupid to throw away his relationship with Beckett because his ego was bruised.
After working their way through gangs who represent every country in the U.N. Castle and Slaughter end up talking to a group of Mexican gang members who all pull their guns. Ryan (Seamus Dever) and Esposito show up because they have been tracking Castle by his cell phone GPS, and blast Salughter for his bad police work. Slaughter has put the “weak link” of the gang in the trunk of his car to scare him into talking. When they interrogate him, Castle realizes that Slaughter is feeding the gang member lines so that he will implicate the gang’s leader, Velez. Slaughter says it’s worth it because they are going to get a terrible criminal off the streets. Castle decides he can’t let this miscarriage of justice happen, so he seeks Beckett’s help.She refuses to get involved because it’s not her case. Still, she hands him a surveillance photo which proves that Velez couldn’t have done it because he was driving at the time of the murder. Castle and Beckett go to the crime scene and figure out the Glitch’s father killed him and get a confession.Then Beckett tells Velez that if he doesn’t leave town the NYPD will be after him, making his life a living hell.