Delirium's Mistress

A recognized master fantasist, Tanith Lee has won multiple awards for her craft, including the British Fantasy Award, the World Fantasy Award for Life Achievement, and the Bram Stoker Award for Lifetime Achievement in Horror.
The fourth installment in Lee's breathtaking series, Tales from the Flat Earth, Delirium's Mistress returns to a shadowy and mythic world where demons battle for dominion, and the fate of mankind is shaped by the whims of capricious and volatile beings.
Beneath the mortal realm of the Flat Earth, demons lurk. But Azhriaz-daughter of the mortal priestess Dunizel and the demon known as Night's Master, Azhrarn-bridges these two worlds, a being of both light and darkness. Raised on an isolated isle in the demons' realm of Underearth, guarded and hidden away from demon and mortal alike, Azhriaz was meant to sleep forever, never knowing the world outside her dreams.
But other forces in the Underearth are moving to wake Azhriaz. Prince Chuz, the demon known as Delusion's Master, has made an enemy of Azhrarn, after his betrayal cost Dunizel her life. Chuz seeks out Azhriaz's island, drawn by her latent power and entranced by her beauty. To release Azhriaz from her eternal slumber, Chuz must create the grandest illusion he has ever rendered. If he succeeds, Azhriaz will be reborn as Delirium's Mistress, a sorcerous of extraordinary power. Perhaps even more powerful than Azhrarn himself....
Delirium's Mistress in the fourth book in the Flat Earth sereies.