Castle and Alexis are on a plane heading for London. There’s a bit of turbulence on the OceanicAir flight. Castle tries to take his mind off this by going over his itinerary. He’s bummed when Alexis reveals that she has plans that don’t involve hearing him speak. Then some really rough shaking cuts short a video-call with Beckett.
The pilot of the plane tells Castle that the air marshal on the flight, Kyle Ford, reported a security issue before he went missing. There are no police officials onboard to help out, so obviously a mystery writer is the next best thing. Castle does a search of the luggage area where a dead Air Marshal Ford is found. He’s been murdered and his gun is missing.
Beckett and the boys work the case from the ground. It’s up to Castle to reconstruct Ford’s movements in the air. Alexis will help, too. She learns that the killer was likely left-handed. As for Castle, he finds video of Air Marshal Ford scoping out a passenger named Isadore Baldon. However, the man sitting in his seat is an imposter. Castle believes they have found their killer.
The Syrian man posing as Baldon is a student named Aiman Haddad. The guy has affiliations with ISIS. Once Haddad realizes he’s been identified, he locks himself in a bathroom. He makes a phone call to someone stating that it will all be over soon. Not good.
The search is on for Haddad’s luggage. Alexis and flight attendant Debbie find his bag, but there’s nothing that suggests he’s a terrorist. Haddad claims he was flying under an assumed name so he could visit his sick mother. He saw Ford texting from a second cell. That phone is tracked down. Castle uses the dead guy’s fingerprints to unlock his phone. There are texts threatening to take down the plane.
Forms are handed out to determine which passengers are left-handed. Marilyn Singer is a former executive with a grudge against the airline. She signs her form with her left hand. Castle finds a gun in her purse. Marilyn denies that the gun belongs to her. She’s genuinely shocked when she learns that her boyfriend, Kyle Ford, is dead. She thought he was cheating on her, but she didn’t kill him.
Castle believes that it’s possible that someone set up Marilyn Singer. Someone wants everyone to think this is over. Victor Deitrich is a wealthy German industrialist who recently sent Ford just under $10,000. The guy says he paid the air marshal for protection for a $13 million watch. Ford was backing up his courier, who was drugged.
The watch was stolen by someone who knew the passenger manifest. This was an inside job pulled by flight attendant Debbie. After 30 years, her pension with the airline was eliminated. No one was supposed to get hurt with her plan to steal the watch. Alexis is able to talk the desperate woman into surrendering her gun.
Castle is very proud of how brave his daughter was in dealing with Debbie. He’s happy to hear that she has reconsidered her plans. She now wants to stick close to her dad. As for Beckett back in New York, she lets out a sigh of relief once she sees online that the people she loves have landed safely in London.