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.

The victim's corpse is found burning in a barrel by a homeless man. The team finds out she worked for US Senator William H. Bracken, whom Beckett holds responsible for her mother's murder. But he seems to be the target, this time. Only Castle learns that Beckett considered holding back evidence before another clue leads the team to prime suspect Robert McManus, a mechanic who blames the senator for his son's suicide. The senator is hell-bent on holding a high-profile speech in a hotel to launch a career-crucial environmental bill.