04E16 - Linchpin

CIA agent Sophia Turner kicks Castle and Beckett of the investigation since they didn't contact her about Blakely. However, she turns up in Castles's apartment with more information for them to investigate, explaining she had to put on a show by letting them go. Thomas Gage reappears, and saves Castle and Beckett and attempts to convince them of his possible innocence. But before anything else can be done, they are found by the CIA and Gates is captured and detained at the secret CIA base. When the girl who seems to be the lynchpin to an apocalyptic event is identified as the daughter of a very influential Chinese tycoon and party king-maker, Gage is killed and a possible mole escapes. Thereafter, Castle and Beckett must try to save the girl's life while dealing with a clever and elusive traitor.