The Doors of Oerth
The Codex of Infinite Planes
A Codex is so massive that two strong men can barely lift it. Tzunk used a paired set of beings called dyophs to carry it around for him. The cover of the book is obsidian and the pages are sheets of paper-thin lead. Each page is inscribed with writings in alien languages and illuminated with illustrations both beautiful and horrific. No matter how many pages are turned, there is always at least one more.
In the Dictionary of Pain, the entry for the Codex of the Infinite Planes appears between the sharp sting of discovery and the salted wounds of failure.
All powers of the book are triggered by reading it, if one knows the proper page in which to look. The Codex can open a portal to any plane, demiplane, or world, at any location. It can summon a greater fiend to serve for a day, and it can raise the dead.
Those who have used the Codex have been known to slowly become more than mortal}, transforming into very minor godlings or fiends. The archmage Tzunk, after lengthy exposure to the tome, gained a horrific form of immortality that caused him to remain conscious and animate even after his body was dismembered and scattered across the world.
The Codex of the Infinite Planes is as much a bane as a boon, and terrible destruction has been unwittingly released against those who attempt to master it: earthquakes, storms, fiendish invasions, imprisonment, and death. Those who even open it for the first time are most often instantly annihilated.
The Codex uses those who think they own it as slaves, entering their dreams and guiding them on visions of the infinite planes, forcing them to write its pages. This is how the Codex continues to exist and to grow. Eventually its scribes use up their own lives; when they come to the page that describes themselves, they are empty husks, and the Codex finds another slave to continue its self-creation.
The origin of this tome is thought to predate the invention of written language among humans. It was discovered by the High Wizard-Priest of the Isles of Woe and used to create an empire on both Oerth and other planes of existence before its powers sank the isles beneath the sea.
It was hoped, then, that the Codex had been destroyed as well, but this was not to be. The archmage Tzunk surfaced with the Codex and, after lengthy study, attempted to conquer the City of Brass. Despite his power he was no match for an army of four million efreet, and he was duly punished.
After the dismemberment of Tzunk, the book eventually passed to the infernal godling Schaethreth, who held it in his possession for over a hundred years. During this period the Codex haunted the sleep of the mage Fallendor remotely, forcing him to write further pages in his dreams, until he escaped by writing his memories on the skin of a paladin from another world. It was stolen from Schaethreth by the agent retriever Regalid Maethos, who hid it within the ruined tower of Kerleth Helvetius, an ally of the efreeti sultan. As of 591 CY, the Codex was being held on the Elemental Plane of Fire.