Members of The Knight Order were paired up with a "brother" or "sister." The entire Order was very close, but a knight's partner grew to be seen as family. Jace's partner, "Cain," was actually Diego undercover, who infiltrated the Order for the Eagles.
The Order was weakened after King Adrian's death. One night, the knights received an anonymous tip about some illegal dealings occurring with the Eagles. Without considering whether it could be a trap, the knights split into groups to find the spots of the illegal dealings. The Eagles attacked the post while the groups were out with professional archers, annihilating The Knight Order. The plot to wipe out the Order also involved the Silver Order, although it is not entirely clear what role they played. In Chapter 1, Aida is ordered to bring a note that links Synius, Kael's advisor, to the "cleaning" of the Knight Order.