Investigating the murder of a thief, Castle and Beckett are surprised to learn that Esposito has a personal connection to the suspected killer. Another surprise is in line for Castle when Beckett hits it off with the handsome Robbery detective assigned to the case, Tom Demming. Now this romantic triangle must work together to solve the case

A high profile chef is found frozen to death in the kitchen of a hot New York restaurant. Complications ensue when Castle and the restaurant owner, an old high school girlfriend of Beckett's, share an attraction. Meanwhile, Beckett's relationship with Det. Demming continues to grow.

A robbery-homicide prompts Beckett to invite Demming to assist on a case, giving Castle a ringside seat to their budding romance. When it becomes clear that the two men have very different ideas about how to proceed, the investigation becomes an unspoken competition for Beckett's attention, one in which each man races to solve the case, as Beckett referees between her two admirers.

Nothing is as it seems when Castle and Beckett investigate what appears to be the assassination of an intelligence operative. Meanwhile, Beckett's romance with Demming threatens her relationship with Castle, forcing them to confront their feelings for each other.