Delusion's Master — Tanith Lee

When the world was flat and the gods had not yet restructured the universe, the cities and hopes of mankind hung upon the whims of the immortal lords of all diabolical powers.

For these, such as Azhrarn, Night's Master, and Uhlume, Death's Master, the world was a flesh-and-blood playground for all their strangest desires. But among those demonic lords, the strangest was the master of madness, Chuz.

The game that Chuz played with a beautiful woman, with an ambitious king, with an ancient imperial city, was a webwork of good and evil, of hope and horror.

But there was always Azhrarn to interfere--to bend delusion to a different outcome--and it was a century-long conflict between two vain immortals with women and men as their terrified pawns.