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.

Beckett and Castle are faced with a large list of possible suspects when a personal injury attorney known as Richie "The Pitbull" Falco is murdered; a shocking secret deepens the mystery surrounding Richie's death.

A death occurs in the woods and Castle becomes obsessed with the case because it reminds him of a pivotal event in his childhood. Beckett reaches a turning point in her life.

After an armored car driver is killed and some of the money it was carrying stolen, details of the heist start to ring a bell for Esposito regarding a previous theft of gold coins nine years earlier. Also, Beckett officially moves back in with Castle but is starting to feel that Castle's home network AI, Lucy does not have as much love for her as he does.