Castle and Beckett escape their car after it gets pushed off the docks into the water.
Ryan and Espo search chess parks for players of the professor. One played him several times and led them to where he lived. In his apartment, information is found about the linchpin and the outcome of the domino effect. The linchpin is the daughter of a major Chinese businessman with the outcome being World War III.
Gage finds them at the apartment and pulls them out as someone starts shooting inside the room. Gage tells them he is not the bad guy and there is a mole in the CIA.
The three are taken back to the agency where Gage ends up dead. Sophia blames her partner, Martin Danberg, as the mole.
Castle and Beckett continue to work on the case and are taken by Sophia to the building where the Chinese businessman and his family were. In the basement, Sophia admits to being the mole and is not an American. Danberg had followed them and killed her.