A body is found floating in the East River on this episode, which leads Castle and Beckett into old tunnels and passageways of New York City. Once there, the partners find a secret from the days of Prohibition.
Beckett: (Clears throat) Ahem. What's the deal with men and boobs, anyway? Castle: Biological. We can't help it. Beckett: But doesn't it bother you that they're so obviously not real? Castle: (Pauses) Santa's not real. We still love opening his presents.