It's a hectic night in the kitchen of the swanky restaurant where billionaire Eric Vaughn is enjoying dinner with business associates. No one notices a mystery figure spray a substance onto one of the meals. The tainted dish is delivered to Vaughn's table. Moments later, Arthur Felder, a wealthy venture capitalist, keels over after a few bites of his dinner. Elsewhere, Beckett oozes sexy as she tries to lure her mystery writer boyfriend into the bedroom. Too bad Castle is super-involved in a heated video game match with a kid from India. Beckett is stunned. Has her relationship with Castle hit a plateau? More on that later.
Castle is impressed when he sees Eric Vaughn at the murder scene. The guy is number eight on his “last supper list.” That's a rundown of people in history you'd like to have at your last meal. Castle's guests include Lincoln, Einstein, Ian Fleming, John Lennon, Joan of Arc, Sinatra... Oh, and Beckett's invited, too. Speaking of Beckett, she's also awed by the charming billionaire in the room. Vaughn says he's been doing business with the victim for years. Castle notices that Beckett may be thinking about putting this guy on her last supper list, too.
A busboy, Cory Harrison, tells Ryan about a short guy he didn't recognize brushing past him in the kitchen. It could've been the killer. A waiter lets the team know that he messed up his dinner order. The victim was supposed to get the squab. Instead, he was given the poisoned quail. Felder wasn't the intended target. Eric Vaughn was. The billionaire knows that whoever was trying to kill him is still out there. He wants Beckett... for protection, that is. Castle is understandably jealous. He can't believe the department is forcing Beckett to hang with some womanizing rich guy against her will. That never happens, right?
Castle knows the quicker they solve this case, the faster he can get Beckett away from the handsome billionaire. Vaughn's attorney, David Anderson, pushes to keep the business going forward despite all that's happening. He's worried that Arthur Felder's funding will disappear now that he's dead. The poison that killed him was created in a lab that Vaughn owns. His top researcher, Cindy, got upset recently when her boss rejected her advances, but she swears she would never hurt Vaughn. Castle follows another lead. He believes Cory Harrison is involved in the murder. He's right. Esposito and Ryan find the busboy shot to death in his apartment.
A bottle found in Cory Harrison's apartment contains the toxin that was used to poison the food. The killer who was in cahoots with the busboy killed him to tie up loose ends. Vaughn is still in danger. That's why he and Beckett check into a safe house. Actually, they check into a luxurious hotel suite. Beckett puts the kibosh on a room service meal, but she does let Vaughn have some champagne. The billionaire almost loses an eye when he pops open the bottle. Beckett helps heal his wound with some ice. Then she joins him for a little bubbly.
The team realizes a mystery man was forcing Cory Harrison to kill Vaughn by threatening his daughter. They can't get a clean look at the guy's face on surveillance video, but the slug pulled from the busboy help ID him as a professional killer named Thomas Barber. Beckett orders Ryan and Esposito to track down this lead as she continues to watch Vaughn closely. She admits that she's with Castle, but pauses when asked how serious it is. Vaughn sees this as an opening to lean in to kiss Beckett. BANG! BANG! Two bullets pierce the window inside the hotel room barely missing both Vaughn and Beckett.
Ryan has Beckett show him where she was standing when the first shot rang out. Castle notices that she was in close proximity to Vaughn. Very close proximity. The only reason the killer missed is because of the kiss. Beckett swears it didn't mean anything, but Castle knows that Vaughn is still alive because Beckett didn't push him away. As for the case, the team learns that Cindy was in contact with Thomas Barber. She didn't know he was going to use the toxin she supplied to hurt anyone. The money she was paid was authorized by Eric Vaughn. Castle believes he orchestrated everything to kill Arthur Felder.
The theory is that Vaughn killed Felder to keep him from learning that he was investing millions into a fraud company. The billionaire denies this. Beckett learns that her kissing suspect is, indeed, innocent. His lawyer, David Anderson, is the one who lost tons of money using the fraud company. The attorney fesses up and Thomas Barber is caught trying to flee the country. Cased closed. As for Vaughn, he realizes that a future with Beckett is not in the cards. Castle is happy about this. He's also taking Vaughn off his last supper list.
Martha believes that without a ring on her finger, Beckett can't really be totally committed to a relationship. This bit of motherly wisdom along with everything that went down during the case has Castle taking action. He snips the cord on his video system as a symbolic gesture. He has a romantic evening in store for Beckett, who asks where they are going. Castle replies that they are going to the bedroom. By the look on Beckett's face, that's not the answer she was looking for.