An Egyptian national, Sara El-Masri, is kidnapped and her bodyguard killed. During the course of the investigation, Castle finds out Alexis is kidnapped along with her. After pinpointing their location to a farmhouse in upstate New York, the FBI raids the house and finds it empty except for the kidnapper, who was tortured and shot to death. Alexis escapes confinement and contacts Castle. The FBI traces the call to a phone tower...in Paris.
While Castle and the El-Masris are being briefed on who was found at the scene of the kidnapping (an older-looking white guy) and what the FBI is doing to get the girls back (attempt to work with the French government), the kidnappers call with a ransom demand: 3 million euros, which the El-Masris immediately consent to. The drop is made in Paris, and Sara is saved...but Alexis isn't. This demoralizes Castle, who tells Beckett he's going home. But later that night, when Beckett returns to Castle's apartment, she discovers he's not there, and Martha assuming he's with her. Instead, he's taken his passport, having gone to France to get his daughter back.
Castle meets with a French official he knows to try to get him to show him to a secret contact he knows. Reluctantly, the official obliges, and gets him in touch with one Jacques Henri, a "recovery expert". He and his colleague are able to pinpoint what building the call came from and infiltrate it; unfortunately for Castle, Alexis was moved from the location. Henri, however, finds they're being watched and gets them to agree to meet with him (and only him) to negotiate a ransom.
In New York, the cops get a warrant for Roger Henson's apartment, but discover it's been looked through before. They find a hard drive, but it's been wiped clean. Questioning the neighbors reveals the same old white guy that was at the farmhouse, and later FBI techs are able to get pictures off the hard drive: pictures of Alexis. She wasn't caught up in another kidnapping; she was the target.
Back in France, Henri has arranged for Castle to bring a 10 million euro ransom to a wooded spot in the hills, but once there, Castle is caught in a setup: Henri turned when he found out who they had kidnapped, and brought Castle there to be shot by the kidnappers' henchmen. But before they can, all five of them, including Henri are shot dead...by the mysterious old man (James Brolin), who spirits Castle away (after shooting his phone after Beckett tells him Alexis was the target). He gives Castle the name Jackson Hunt (which he admits is an assumed name).
Once the pair get into a secure location, Hunt gets a call from an old "friend": internationally-known crime boss Gregor Volkov (known enough for Castle to have him be Derrick Storm's arch-enemy), whose wife Hunt killed on a mission a dozen years ago. Volkov holds a grudge, and offers to turn Alexis over in return for his own life. Castle wonders what interest the old man has in Alexis (he has dozens of pictures of her), and Hunt says that she's his granddaughter...and that he's Castle's father.
Castle doesn't believe him, but he gives him a memory: when Castle was 10 years old, looking for a book at the New York Public Library, a man pointed him to a copy of Casino Royale, the book that made him want to be a writer. Hunt says he was that man and that he helped Castle gain access to the CIA for research for things he wrote in his novels. Now convinced, Castle asks Hunt to come up with a plan, which Hunt responds to by giving diagrams and blueprints of the complex where he knows Alexis is kept, and the plan to get at Volkov.
That night, Castle infiltrates the complex through the sewers and plants an explosive that would take down the place's power...but he's caught by Volkov's guards and marched into the room where Alexis is being kept. Volkov takes Castle's radio and tells Hunt he has ten seconds to come out, or he shoots Castle. Hunt tells him he's not going to kill Castle...because he's already dead. At that moment, the radio explodes. All part of the plan. Castle breaks Alexis out of her cell in the commotion and they both run like hell out of the complex and to the American embassy. Before the pair put the plan into motion, Castle wonders if he'll know Hunt survived the mission. Hunt says he won't, but if he does, he'll try and contact him in the future.
As the pair return to New York, they're greeted by a Welcome Home party thrown by Martha and Beckett. Beckett warns him to never do anything like that again without her. As they celebrate, Castle spots an envelope on the table that arrived that morning. Inside is a copy of Casino Royale. And despite being instructed not to give out any details, Castle feels compelled to tell Martha a small snippet.
Tropes
- Cutting the Knot: "What about his men, won't they try and stop us?" "Don't let them."
- It's Personal:
- Beckett loses it and kicks a suspect/witness out of her chair, screaming that her partner's daughter is missing and today, she is not a cop.
- When Castle's French expert says maybe it's not the place and Castle shouldn't come along?Castle: My daughter. My money. I'm coming.
- Papa Wolf: "You are emotionally compromised. That makes you like an animal. You are dangerous to them."
- Castle's dad has been watching him his entire life. He had to stay away to keep his son safe, but he came out of hiding to save his granddaughter. He even inspired Rick to become a writer by giving him a copy of Casino Royale when he was a kid.
- "Well Done, Son" Guy: Richard finally meets his father, and he learns his father couldn't be more proud of him.
- Wham Line: "Because she's my granddaughter. Richard, I'm your father."
- Wham Shot: The episode ends with Castle opening a package containing Casino Royale, original edition, and telling Martha "Mom, there's something I wanna tell you."
- What the Hell, Hero?: Castle opens the episode screaming at the El-Masris, only for them to tearfully beg him to stop, because their daughter was taken, too.
