Fortress of Dragons by C. J. Cherryh

The walls between the worlds are down. A new unfolding has begun...

It started long ago, as a war between the shadowy Immortals that persists today, as the wizard Mauryl's Shaping confronts the Shadows summoned from Chaos. Tristen is that Shaping. Both more and less than human, he successfully fought sorcery's evil tides, a victory that brought his friend Cefwyn both a kingdom and true love.

But the Lines that hold the world in place are shifting again. A ruthless enemy is preparing for battle. Once again, Tristen will take up the sword inscribed with "Truth" and "Illusion" on its blade. But he faces more than war and a pretender to Cefwyn's throne. The Shadows he sees are straight from Ruin -- a flow of darkness covering the world like ink...

Fortress of Dragons completes the high-fantasy epic begun in Fortress in the Eye of Time and continued in Fortress of Eagles and Fortress of Owls --a powerful tale set in a world of magic, violence, wonder and awe -- a world as vividly real as our own.