From the introduction:
There are a few things that one must know before reading this Tome.... in it, are the secrets of the damned. These secrets have been lying, awaiting their discovery, for thousands, possibly millions of years. Now, a few brave souls have ventured near enough to them, so that their anticipation can await no longer. Opening crypts and tombs, these secrets have been revealed, and they tend to stay that way. The way of the world as we know it, may forever change. Death, Peril, and Damnation await us behind every corner. But, how does that change the world? No one has seen death as horrid as these, peril as depressing as written here, and no one (or no soul), has suffered any kind of damnation that has been recorded within these pages. Gods and heroes clash in the midst of the abyss, while the undead stalk the Material Plane. Oh, what has befallen the world now?
Tome of the Damned presents a variety of items, class options, spells, and monsters for general campaign use. Most of the items involve evil or undead in some way.