A Hrule is a rare Free Magic creature that feeds on the blood of Charter Mages. It cannot be killed, but temporarily returned to the earth by piercing its hide with a thistle head. Three chains, of silver, lead and braided daises, can apparently be used to render the Hrule immobile. In the novella Nicholas Sayre and the Creature in the Case, Alastor Dorrance, the leader of Department Thirteen serves his "goddess" the Hrule by feeding it the blood of people who bear a Charter Mark. Dorrance planned to feed Nicholas's blood to the creature in the case but his blood was tainted and too powerful because of the free magic in him from The Destroyer.