During the game, someone will case the area on another pretext to determine the location of the keystone. We suspect that it's either in the throne, the ceiling, or the Ophiuchus dorms. Once we know for sure, Orion, Pyxis, and Canis- maybe Lacerta and Cepheus, too, depending- will cause a distraction while Scowl, cloaked so that King can't spot him, takes it and runs. Even if it's the ceiling, he should be able to reach- those shoes he wears let him jump to heights that simulate flying, and they grant him the speed to clear the area quickly afterward, too.