When the world cracks open and the demons attack, what will YOU do? The Book of Demons takes an in-depth look at the Abyssal enemies of the 13th Age - the demonic hordes whose eternal struggle to shatter reality causes hellholes, dimensional breaches, and other, even weirder assaults on the world.

For players, it features a new demonologist PC class, with three paths: corruption, flame, and slaughter. For GMs, it features:
* Six detailed hellholes and their denizens, plus advice on making your own
* A new random demon abilities table
* Citadels of the Crusader and the Diabolist
* Monster stats for nine new demons summonable by player character demonologists