Book of Secrets

Red leather and steel fittings protect the pale vellum pages of this massive tome. The exterior is covered in strange glyphs and runes of the Arcane Language of Magic. Those who can read it get a sense of what this volume contains: the exploitation of the Winds of Magic.

To use this Grimoire, the user must spend three weeks studying the arcane words within. At the end of this time, he may use the book to cast spells from the Lore of Death, Fire, or Shadow. His ability to use magic is amplified while the tome remains in hand. But when he casts spells using this book, he risks suffering from the Curse of Tzeentch. What's worse, each time this book is used to cast a spell, the wielder resolve is tested against mutation. Furthermore, if a servant of Khorne (cultist or Champion) attempts to use this book, the Blood God immediately destroys the wayward mortal.

History
The Book of Secrets contains the writings of a mad Arabyan Wizard who coveted the powers of Elven High Magic. Believing the strictures set forth by Teclis had unnecessarily restricted the potential mastery Human Wizards could attain, he rejected the Colleges of Magic and set forth to master the art on his own. He threw himself into his work dabbling with Aqshy and Ulgu and seemed to succeed in working with both. Drawn to the power he thought lay ahead, and not noticing the side effects he developed from working with Dark Magic, he threw himself into the Lore of Death. Then, nothing was ever heard from him again. Some believe this madman was drawn into the Realm of Chaos or even murdered by Elves. But those who have pored through the Book of Secrets claim to hear faint cries for help coming from within the very pages of the tome...

Source

 * Warhammer Fantasy RPG 2nd ED -- Tome of Corruption (pg. 180).