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.

After tracking a killer to his apartment, Beckett steps on a bomb trigger and must stand in place while the bomb squad finds a way to defuse it. Castle stays with her, and they argue over who liked who first, via flashbacks.

While Beckett is out of town, Castle becomes involved with Detective Slaughter in a case where a hi-tech chip has been stolen and one of Slaughter's informants is murdered.