On the Rim of the Mandala by Paul Cook

Lou Colleran is an immortal. But even immortals can be killed. For the universe is being threatened by genetically designed creatures called calibans. And the only thing between them and the destruction of the worlds of the Mandala is Lou Colleran.
But can Lou Colleran, an immortal haunted by a woman dead hundreds of years, and preoccupied by seductive dreams, survive long enough to save the universe from destruction?