Terry Pratchett's Hogfather

In Discworld, it’s the night before Hogswatch. You know, that special night when the Hogfather delivers presents to the kiddies. What the Hogfather doesn't realize is that he’s being watched by the Auditors—the Discworld’s grey-robed specters who audit not money but the entire universe and maintain the neat order of things. They’ve formulated a plan to destroy human belief so that there's not an atom of it left and the Discworld can finally be theirs.