Castle finally gets Beckett, who admits so only in therapy, she may have made him wait too long when he teams up for an investigation with her colorful colleague detective inspector Ethan Slaughter, a cowboy style bulldog, who was assigned multiple decapitated Jamaican corpses from the Irish Westies gang member Brian Reilly's maverick son. Although uncomfortable with the ruffian style, gentleman sleuth Castle proves his value while they discard a simple gang war and focus on newcomer Cesar Vales's Mexican gang. Castle not only repeatedly appeals to his former team, but actually turns to them when he disagrees with Slaughter's theory as well as his bully blackmail method.
- Awesome Mc Cool Name: Detective Slaughter.
- Cowboy Cop: Slaughter takes this trope up to eleven and shows how shitty it really is.
- Friendship Moment: Though Ryan and Esposito demand favors from Castle when he asks them to run plates and fingerprints, the second they learn he's in trouble they roll up. Likewise, Beckett keeps tabs on the case and has Ryan and Esposito run deets to keep Castle safe from Slaughter's bullshit.
- Papa Wolf: Slaughter talks about the hot little redhead intern at the morgue. Castle lets him know she's his daughter. Slaughter keeps talking. Castle decks him.
- Special Guest: Fillion gets to reconnect with an old friend, Adam Baldwin as Detective Slaughter.
