The Six Terrible Books of Earth
These books are banned by every human nation on Yrth, both Christian and Muslim. But somebody keeps printing them; and no matter how often the Ministry of Serendipity burns the Books, there’s always another popping up. Usually just before something explodes, or burns down, or sees an uptick in Mob violence. The average mage of Yrth reacts to the Six Terrible Books of Earth the same way that an Arkham professor reacts to a Mythos tome, and for the exact same reason: they inexorably corrupt the status quo. Thankfully, they’re all written in English, which is difficult for Anglish and Arabic speakers to understand.