The Dark Shore by A.A. Attanasio is currently free to download from Amazon (US, ES). This is the synopsis of the book:
Here is an epic fantasy from the dawn of Creation, from the first worlds, the Bright Worlds. Among them is Irth. And upon Irth, in a realm of wizards, witch queens, and magic, destiny casts shadows into the Gulf and onto the Dark Shore, a universe of blacker magic and deeper mysteries -- the greatest of which is Earth.
Irth is a world where magic rules -- magic that radiates from the Abiding Star. The nobility, possessors of most of this mystic energy, dwell in floating cities that drift above their realms, plotting against each other for domination.
Those who fail in their attempts to hold or usurp power are cast off the Edge into the abyss beyond the reach of the Abiding Star. There they fall into the cold world of the Dark Shore -- onto Earth -- from whence no one has ever returned. Until now.
Hu'dre Vra, formerly an abject scavenger who found a magical sword but failed to use it wisely and was cast into the abyss, has returned from the Dark Shore with an awesome new power: black magic. At the head of an army of cacodemons impervious to Irth's enchantments, Hu'dre Vra the Dark Lord wreaks a terrible vengeance upon the world that exiled him.
But there is resistance to the Dark Lord's rule of terror. The mysterious, inventive thief Ripcat and his crafty partner Dogbrick form an uneasy and dangerous alliance with the brave young noblewoman Jyoti and her small band of comrades, among whom is her family's ancient sorcerer, Caval. Together they all must pit their courage, their wits and their lives against the brutal minions of the Dark Shore.
A magically charged and enthralling tale of a once-charmed world and the supernatural evil that threatens to destroy it.