Book of Magnus
"The ancient knights' quest for the Grail, the alchemists' search for the Stone of the Philosophers, all were part of the Great Work and therefore endless. Success only opens up new avenues of brilliant possibility. Such a task is eternal and its joys without bounds; for the whole universe and all its wonders...what is it but the infinite playground of the Crowned and Conquering Child, of the insatiable, the innocent, the ever-rejoicing heirs of the galaxy and eternity, whose name is Mankind?"
- – The first line of the Book of Magnus
The Book of Magnus TM is Magnus the Red's Magnum Opus (Ha! Get it! Magnum as in Magnus! *BLAM*) is a monumental tome of sorcery compiled by Crimson Cyclops from the arcane lore he gathered from all across the galaxy during the Great Crusade.
Overview
The book was written by Magnus through his personal scribe Mahavastu Kallimakus. Later during the Horus Heresy, the Daemon Fateweaver manipulated Hathor Maat into altering a single line on the book.
The original still exists within the library of the daemon-primarch Magnus, atop the Tower of the Cyclops on Sortiarius and Magnus takes it with him when he strides to war or he finds some interesting shit to nerd out on and take notes. The book has several copies - one of them is with Ahriman; taking a copy before his exile, while another copy is said to reside in the Black Library of Chaos. How the Harlequins managed to get a copy from Magnymagick, we have no idea, possibly due to a bit of clownery.
The Book contains the single-largest reservoir of warp-based knowledge and sorcery; featuring anything from the mundane (Like how Warp entities work) to the esoteric and forbidden (Answers to the Sensei). Nothing comes close to it in terms of sheer knowledge. Of course the Book of Lorgar may possess more info on the Chaos Gods and various daemonic summoning rituals, but it also reads like some sort of horrid fan-fic. The Book of Magnus being a collection of PhD papers, thesis and other boring nerd stuff, is at least dry enough that you won't accidentally summon a daemon from your own asshole by flipping to the wrong page.
An interesting point of trivia, but since his fall, the pages from the Book of Magnus has known to change by itself to whatever the reader wants to know off; flipping pages by itself or self-translating itself to various languages. Pretty god damn convenient. Of course, the book is never finished as Magnus is still busy exploring the Empyrean, but given the book's ability to literally condense info by itself to gain more writing space, paper has never ever been an issue.
