The Sunset Warrior (The Sunset Warrior Cycle, Book 1)

Ronin called no man master.
He was the finest swordsman of the Freehold, as sharp and deadly as his blade. Yet as the ancient city faltered, Ronin alone refused to pledge himself to any of the powerful Saardin who ruled the crumbling underground world of levels.
But now dark magic was loose in the world. As the ravings of the Magic Man foretold doom, Ronin and his lover, the sensual K'reen, were swept into a maelstrom of treachery, violence, and sudden death.
Their only hope lay in the lost scroll of the Ancients. And the desperate search led Ronin down into the very bowels of the earth, and up again, to the barrier of Freehold, where the endless ice began . . . .