The central twist in the plot is the reappearance of Cynthia Heat, Nikki's mother, after 20 years, whom Nikki glimpses on the street but cannot track down. Her emotions about discovering that her mother has chosen to be absent from her life for unknown reasons are similar to Castle's feelings about his unknown father, as particularly expressed in Target and Hunt.
At the end of the book, Nikki moves out of Rook's apartment temporarily while she focuses on tracking down her mother, in the same way that Beckett leaves Castle to solve the LokSat case in XX. As Castle does in the episode, Rook says: "If you have a problem, we have a problem. That's how this works." And, like Beckett in the episode, Nikki answers: "Not this time."