Beckett senses that something's up with Castle. It's as if he's pulling away. That's probably because he is. Lanie actually gets Beckett to admit that's she crazy about her partner. So tell him! She can't. There's a murder that needs solving. Yeah, yeah. There's always a murder that needs solving. The bigger problem for Beckett is the fact that Castle just jetted back from a wild weekend in Vegas with a pretty flight attendant by his side. As for the case...
We jump back a few hours to see a young woman dead on a bed inside a seedy hotel room. An unidentified man swipes something from the lining of her jacket. He inexplicably gives the victim a kiss on the cheek before escaping past a chambermaid. In present time, we learn the victim is Naomi Allen. She's a British model who had been booking gigs that connected her with wealthy men. Her latest event was an album launch party. Beckett thinks this may be the place where she met her killer.
A fingerprint at the victim's apartment belongs to a man who matches the murder suspect's description. Beckett finds the guy stepping out of the shower in his hotel room. She orders him to reach for the sky causing his towel to fall to the floor. Castle tries to cover Beckett's eyes, but she manages to sneak a peek at her handsome, naked suspect. The guy happens to be Detective Inspector Colin Hunt of Scotland Yard.
Colin Hunt had known Naomi Allen since she was a kid. Her dad was his first partner. He found a key in the lining of her jacket. It was a message to him about the identity of her killer. Hunt is permitted to work the case with Beckett. That's fortunate since Castle has a lunch date with his pretty flight attendant. He skips the interrogation of a female rapper who had an altercation with the victim at the album launch party. The singer thought Naomi was making moves on her main man/manager: Biggie Slim.
Biggie Slim says Naomi claimed someone followed her to the party. The killer left a partial print on the victim's neck. Lanie needs a full print from the killer to make a match. The mystery key Hunt found on Naomi belongs to a gym locker. It contains a number sequence written on the back of a photo of a man who may be the killer. He is Nigel Wyndham, the Deputy General of the British Consulate. This case just went international.
Getting a fingerprint from a foreign dignitary won't be easy. Fortunately, Castle has a plan which involves rappelling down a building with a Romanian gymnast he found on YouTube. Love it! Beckett and Hunt have a better idea. They'll crash a party at the British Consulate. Castle can't help but notice how stunning his partner looks as the equally-dashing Detective Inspector Hunt escorts her out of the precinct.
There's some obvious heat between Beckett and Hunt as they exchange life stories on the dance floor. Both admit they are married to their job. Beckett then gets a new dance partner in Nigel Wyndham. All attempts to snag his fingerprint-friendly drink glass go south just as Hunt is exposed as a party crasher. Beckett is asked to follow him out the door but not before she swipes Wyndham's business card case. Unfortunately, the prints on it are not a match to the killer's.
With a little help from his flight attendant, Castle is able to crack the number code written on the back of Wyndham's photo. It's refers to a diplomatic pouch that was delivered via airline. It's traced to a flight that went to Uganda, which happens to be the place where Naomi's boyfriend was killed by guerilla forces. Hunt sneaks into JFK's secure baggage area to learn that the shipments were for stinger missiles. Wyndham was smuggling them into Uganda. That's why Naomi was trying to get close to him. She was killed by his partner in crime: Biggie Slim. Both Slim and Wyndham are arrested. Case closed.
Lanie has a heart-to-heart chat with Beckett. She urges her to tell Castle how she feels before it's too late. To Beckett's credit, she attempts to do that several times during the case. It just doesn't ever pan out. Beckett later turns down Colin Hunt's offer to join her for a drink before he heads back to London. She wants to talk to Castle, but he's off to spend more time with his uncomplicated new lady friend. Guess that's why Beckett then calls Hunt. She'll be having that drink with him after all.