Season 4 | Episode 416 | Aired 02/20/2012
Castle realizes that a photo of a young Asian girl is the first domino that will fall. She’s the linchpin. He’s about to call Sophia when a gun-wielding Thomas Gage orders them to run. He leads them out of a firefight as unseen assailants with automatic machine guns attack. Castle and Beckett thought Gage was the bad guy. In fact, he’s the person being set up by someone inside the agency. Speaking of the CIA, they’ve just arrived to take everyone back to the underground headquarters.
Sophia questions Gage about the identity of the young girl. She gets no answers. Chances of a follow-up interrogation disappear when Gage is found shot to death in his holding room. Sophia orders the bunker be put on lockdown. They trace the person who altered the video system in the holding room. It’s linked to an operative, but he’s a decoy. The real mole is revealed to be Agent Martin Danberg, who takes hostage before making a daring escape.
Sophia says that Danberg is likely not working alone. They need to find the linchpin. Castle suggests they use topographical analysis to identify the mountains behind the young girl in the photo. Sophia has a chat with Beckett while the computer does its search. She reveals that after she slept with Castle the tension and longing that had been between them for so long was suddenly gone. That wasn’t a good thing. This newsflash appears to have Beckett feeling even more conflicted.
The young girl in the photo is identified as the daughter of a Chinese businessman, Xiang Ganghong, who is extremely influential in shaping his government’s economic policy. America’s government would shut down if this man used his influence to end China’s purchase of U.S. debt. That could happen if his daughter was killed in a botched assassination attempt that was orchestrated by a CIA operative like Gage. As it turns out, Xiang is currently head to the U.N. for a trade conference. His daughter is also making the trip.