From publisher blurb:
Fell Legions and Insidious Plots
Through subtle plotting and brutal aggression, the forces of the Nine Hells seek to corrupt or dominate all who stand against them. These fiends, as ancient and terrible as any in the multiverse, forge armies out of the souls of the wicked and use them to enforce their iron rule. Can your adventurers stand against the might and tyranny of the Nine Hells?
This supplement for the D&D game presents the definitive treatise on devils and their malefic home. Along with information about the physiology, psychology, society, and schemes of the devils themselves, you’ll find feats, spells, items, and tactics commonly employed by these infernal creatures and those who oppose them. This book also provides detailed information on various devils, archdevils, and the layers of the Nine Hells.