This episode entitled, “Linchpin” continues from where the previous episode left off, which was Castle and Beckett being locked inside a car and driven off a dock into the ocean. The car is slowly submerging into the water with Beckett and Castle inside with both trapped inside the pair try to escape, but with the doors jammed looks like there is little that they can do. Beckett decides the only option left is to shoot out the windows, but her gun is missing and her seatbelt is stuck literally causing her to be tied to the seat. Castle goes in search of the gun diving into the water that is steadily entering and filling the car. He sees the gun, but it is caught underneath the driver’s seat. He tries to pull it out, but after a few attempts he has to get air, he continues to do this for another time, but he never returns back for air. This causes Beckett to panic, with the water completely filling the car she tries to escape from her seat, but cannot no matter how hard she tries. She starts to lose consciousness, but then two gun shots ring out and Castle is pulling them out the car to safety.

Back on land, the two are safe and recovering from their near death experience  when Esposito tries to question about what happened and what have they gotten themselves into. They both say it is classified, but that doesn’t sit well with Esposito. He goes off saying that he was in the “military and ate classified for breakfast,” and how come “writer-boy” aka Castle gets to be in the know and not him. Seems like some is jealous, but nothing gets resolved as Sophia and her team drives on the scene ordering Castle and Beckett into the car.

She takes them back to the CIA, where she publicly scolds them for being so reckless that it their witness killed. Sophia then promptly kicks them off the case and goes so far as to bring up her past history with Castle stating that” he can’t rewrite this ending like he did with them.”  This comes as a surprise to Kate, who thought that nothing of the romantic sort happened between the two, awkward! Kate questions

Castle on his history with Sophia and he says the two slept together thus promptly ending their conversation at that note. The pair makes their way back to the station where Beckett brings up the subject of previous muses, wondering if there were others to her little club. Beckett seems to have a touch of the green eyed monster, with the prospect of Castle having other muses before her. Castle says there was no one else, but Beckett believes that he is lying, but changes the subject anyways back to the case at hand. Castle reminds her that they were kicked off the case, but she reiterates that she is a homicide detective and will solve this case.

Beckett and Castle head to the Medical Examiner’s office to see Blakely’s body, but Lanie informs them that the body was intercepted on the way order, by people with a court order.

With no other avenues to search for the day, Castle makes his way back home and finds Sophia sitting inside waiting for him. Sophia explains that all the yelling and kicking the two off the case was all staged, to make it look good for her superiors .She even hands over info on Blakely’s accounts for Beckett and Castle to investigate, but warns him to stay safe because things can turn at any moment.

Meanwhile, Ryan and Esposito are canvasing local chess games at parks hoping that someone knew Blakely. The two get a quick response by some men saying that Blakely liked to play chess with Yanni. The two find Yanni, who just happens to be an economics professor and advisor, into the station for questioning about the talks that he and Blakely used to have. Yanni say that he Blakely would talk about economic theory and theory, but that was all. He even provides information to where Blakely was supposedly living at.

Beckett and Castle head to Blakely  place and find a series of articles and newspaper clippings connected by string indicating all the major factors leading up to “Linchpin” which has a picture of ten-year old Asian girl attached to it. Out of nowhere Gage appears telling them to run, the pair are startled, but flow Gage’s advice, when an explosive is thrown through window followed by a series of gun shots. They go with Gage who helps them escape. He explains that he has been set up and has been trying to stop “Pandora” from the very beginning, but before he can say anything else, they get caught by Sophia and her men.

Everyone is taken back to the CIA field office where Sophia starts interrogating Gage. He explains that he has been setup and that there is a mole inside the CIA helping the really criminals behind “Pandora.” Sophia says that he is lying, but he says that he saw that man at the docks when Castle and Beckett’s car was driven into the water; he says that man moved like he was in the CIA. Sophia leaves and tells Castle and Beckett not to pay attention to Gage, saying that they have more pressing matters, such as trying to find the little girl who seems to be the start to “Linchpin.”

Sophia gets her team to run a recognition program to try to identify the girl, but with no luck she ultimately has to return back to Gage, the only problem they find Gage shot point blank range through the head. Sophia locks down the building and wonders why no one saw anything, but finds out someone hacked the system.

Through some back hacking they find out it is, Thomas Danberg, Sophia’s partner. With guns drawn, he says that he is innocent and decides to take a hostage as a way out. He escapes via the elevator while he knocks out the hostage.

With little time left as “Pandora” is set to being tomorrow, the team focuses back on finding the girl. Castle recommends that they try for matching up the topography from the picture, instead of the girl herself. While, this is happing, Beckett questions Sophia about what happened with her and Castle. Sophia explains that there was a lot of sexual tension between them and one day they just acted on it, but afterwards they realized they had nothing in common. With hours left on the clock, the CIA identifies the topography and more importantly the girl. She is the daughter of a highly influential Chinese businessman with strong ties to China’s government. If his daughter were to be killed and have it linked back to the United States it could cause major repercussions h that could plummet the whole world into WWIII.

With little time to spare, Sophia, Castle, and Beckett head to the Trade Commissions summit, where the assignation is to take place. Upon, arriving they are met by another CIA agent where they are taken to an abandoned room where Sophia and the agent draw out their guns on Castle and Beckett. Castle and Beckett then realize, Sophia was the mole all along, not Danberg. She is apparently KGB and says that she is purely in it for the money. She yells for the two to kneel and lets it slip that Castle’s father would be so disappointed to hear of his son’s death. The shock on Castle’s face is clearly advent, which gives Sophia pleasure to hear that Castle knows nothing about his father. She goes on to say that he was the reason that the two were able to work for the CIA in the first place and before she can take aim, she is shot dead by Danberg. Danberg and the three stop the agent before he has the opportunity to kill the girl, thus ending the plot to create WWIII.

In the end, Castle and Beckett are debriefed by Danberg who lets them know that all is taken care of. Castle asks Danberg, about the comment Sophia made about his father and he says that he knows nothing that could help. After, Danberg says his goodbyes Castle asks Beckett about her thoughts and she says that they should take comfort that they save a little girl today and that should be what matters most.