From the intro:
"You are in Hell.
For an eternity, there has been nothing in the Infernum except constant war and constant suffering. Those in power grind those beneath them into the burning dust, while those below plot and conspire to overthrow their masters and take their place and all bow before the might of the warring Houses. Now, there is dissent and opposition even against their might, as the Free Cities declare their independence and threaten the hegemony of the Houses.
War is coming to Hell. Anyone, even a mortal, could conquer the Pit and become a lord of the Infernum.
Infernum: Book of the Damned is the Player’s book for the Infernum Roleplaying Game. In it you will find everything you need to start your adventures in Hell and begin working your way up the demonic ladder towards total domination.
Play as Mortal, Demon or Fallen Angel. Equip yourself with the latest infernal weaponry such as the flayer or hellcannon and trap a demon within your chosen tool of warfare. Develop and nurture your mutations as they twist your flesh and increase your demonic power. Feed from damned souls and bind other demons in unbreakable Covenants. Do unto others before they do unto you and remember...
Conquer or suffer. These are the only choices in the Infernum."