The team investigates the case of Sam Siegel, owner of the Sapphire casino in Atlantic City, who was shot and killed at an abandoned dock in New York. By looking at the victim's GPS, they discover that he had made a stop at the apartment of his beautiful ex-wife, Rebecca. Rebecca tells the team that Siegel was indeed there the night before, begging her to sign over her half of a building which they still co-owned, offering her the full price instead of only the money for her half of the building; Rebecca agrees with the neighbors' report of a loud argument, but says that after she refused to sell without consulting her lawyer, Siegel left, admittedly angry at her refusal. The doorman confirms her statement that she was at home for the rest of the night. When the team returns to the office, Captain Gates orders Esposito and Ryan to head for Atlantic City to investigate. For a change, Castle wants to go with Ryan and Esposito rather than staying with Beckett, since he loves Atlantic City, and Gates actually orders him to do so, to his and Beckett's surprise. Captain Gates orders Beckett to remain and run the New York portion of the case, tossing out an odd semi-compliment: she thinks Beckett is a good cop, but believes Beckett can be an even better one without "distractions." As she faces the camera, we see Beckett's face reflecting her amused surprise at the compliment.
On their way to Atlantic City, Castle and Esposito eagerly discuss checking out casinos for Ryan's bachelor party. Ryan has been dancing around that topic rather nervously, and he unhappily breaks the news: rather than his preference, Esposito, he has been compelled to ask his fiancee's 16-year-old half-brother. After coming to grips with that disappointment, Castle and Esposito announce that they will have their own impromptu bachelor party while working in Atlantic City ï¿½ no reason that solving a murder cannot be fun!
Nadine, the special concierge, greets the team and offers any help that they may need; Castle asks her about the night's shows, and it turns out that Sapphire is hosting an Elvis look-alike contest, so the only act is Carrot Top ï¿½ whom Castle adores. Nadine then directs them to Charlie Turner, Siegel's business partner, and they begin to question him. When Daniel Sullivan, Sapphire's head of technical security, briefly interrupts the questioning to report a card-counter to his boss, Turner brags about the casino's facial recognition software. A moment later, Turner himself interrupts to greet a guest who declares loudly that his luck needs to change. Asking the tech specialist for his help, the team uses that software to see if they can discover when Siegel acquired the split lip a few hours before his death. The surveillance video shows that Charlie had punched Siegel in the face, a small fact that Turner had neglected to mention. Back in New York, Beckett brings Siegel's driver, Marino, into the office for questioning. Despite having a record, Marino is eventually cleared. In some quick telephone communication with Beckett, the men learn that Siegel had transferred $10 million from the casino's account to an account in the Caymans a few hours earlier; they assume simple embezzlement, and Turner lets them believe that assumption. Although Charlie thinks that it was Siegel who stole $10 million from the casino, the team investigates further, discovering that Siegel could not possibly have been on line at the time of transfer, as he was "occupied" with a "massage" at the time. The concierge Nadine unexpectedly emerges as the prime suspect. It turns out that Nadine's parents live in the building which Siegel was trying to get his ex-wife to sign over. As the team prepares to take Nadine in for questioning, she is suddenly snatched, only a few yards away, by some unidentified men. At that point, Charlie refuses any further cooperation and has the three thrown out of the casino, threatening them with dire consequences if they return [as New York cops, Ryan and Esposito have no legal standing in New Jersey, and Castle is a civilian]. Obviously, Charlie has been feeding them only half-truths; they have figured out that the money problem is much more complicated than mere embezzlement: it was a loan from the Mob, due to be repaid the day that Siegel was killed.
The scene switches briefly to Castle's New York apartment, where, at Castle's suggestion, Alexis has planned a "girls' night" to help cope with her grief over breaking up with Ashley. Through the wonders of social media, the small party becomes a mob of people whom Alexis has never met; the sheer press of numbers, coupled with consumption of booze and general silliness, begins to demolish the pristine surroundings. Taking firm control of her emotions and of the mini-riot, Alexis sends everyone home and begins a frantic effort to repair all the damage to carpet, furniture, and mementos.
Back in New Jersey, the three men stand disgruntled outside Sapphire, complaining that the sophisticated facial recognition software would spot them instantly if they sneaked back in, Sapphire employees wheel in a rack of Elvis costumes, and Castle gets one of his typical brainstorms: If the three of them dress as Elvis impersonators, they can wear dark glasses, sideburns, and wigs, easily sneaking back into the casino. Once inside, the Elvoids approach tech expert Daniel and learn why he helped Nadine transfer the money. Daniel and Nadine are in love, but Siegel had been pressing unwanted attentions on Nadine, and had threatened to evict her parents if she did not sleep with him. Daniel and Nadine took the money as blackmail, only until Siegel would sign her parents' building over to them, at which point they planned to give the money back. By telling Turner what he has figured out about the mob, Castle gets Turner to admit that Moretti, the man who had called out that his luck needed to change, was the chief mob negotiator. At that point, although the men had tried to discourage her from coming, Beckett arrives at the casino and arranges for Daniel to return the money if he is allowed to see Nadine. In grudging admiration for Daniel's courage, Moretti has Nadine brought into the casino; Daniel transfers the money, and the lovers embrace. Moretti convinces Beckett that not only did he NOT kill Siegel, but he also gave Siegel an extra day, because Siegel had showed him the signed deed from Rebecca ï¿½ who had sworn to Beckett that she did NOT sign it the night before. Beckett has Rebecca brought to the office and presents her with the signed deed, crumpled and dirty from being in Rebecca's garbage, and Rebecca finally tells the truth: Siegel had been a brute for all of their married life, and she had only been able to get a divorce because he said that she had gotten "too old" for him. He had shoved a gun into her mouth and forced her to sign over the deed; then he had made a call to arrange a meet with Moretti. Rebecca retrieved the gun he had given her as an anniversary present, followed him to the meet, and shot him after Moretti gave him the extra day. Gates has listened in to the confession, and assures Beckett that she will apprise the District Attorney of mitigating circumstances when they offer Rebecca a plea. Gates and Beckett have a brief, quiet, pleasant conversation which includes mention of Castle's unique abilities as a non-cop: a clever replay of Beckett's early attitude toward Castle's unorthodox methods, as Beckett insisted ONLY on facts in the face of Castle's creativity. Now it is Gates who insists only upon facts, and Beckett who points out how very useful a different outlook can be.
As the story closes, the exhausted Alexis, who has been working at top speed all night to repair the damages of the "party," sits quietly beside the even-more-exhausted Castle, each assuring the other straight-faced that everything is "fine."