Sha-Nazen by Heather Wielding
The world has changed, and with it, magic itself has altered. White and dark are no longer bound, and those who once knew the ways of might, can no more command it. In this changed realm, Br'non seeks after his lost love, unaware of her being trapped in a life-threatening Game. As the Empress rises to dominate all known realms, even the mightiest of wizards stand helpless. A dark force has risen, and the Balance of the Universe nears its final destruction.
And all the while, something small and very grey, walks unseen. Will a shadow prove to be mightier than all the forces of the Universe combined? Or will the Balance fall into darkness, leaving all known realms to ruin...