“You know how they make fabrials, don’t you?” Taravangian asked. “Enslaved spren?” “Spren can’t be ‘enslaved’ any more than a chull can.” The Stormfather rumbled distantly in his mind. “That gemstone,” Taravangian said, “imprisons the kind of spren that gives things substance, the kind that holds the world together. We have entrapped in that shield something that, at another time, might have blessed a Knight Radiant.”