Blackmantle: A Triumph (Keltiad) (1997)

Amazon.com Product Description (ISBN 0061056103, Mass Market Paperback)

Once, in Keltia, a woman dared to wrest back from the Lord of Death himself the greatest treasure of all: her beloved mate . . .

It is a time when the star-kingdom of Keltia is plagued by the Firvolgi, an ancient alien race. Yet along with a problem, the gods have sent a solution: Athyn Cahanagh, born orphaned on a battlefield, becomes High Queen and drives the invaders out. Athyn--now known as Blackmantle--and the great bard Morric Douglas fall in love and wed, ascending the Keltic throne as king and queen. But the lovely, dissolute courtesan Amzalsunëa vows she would sooner kill her onetime lover Morric than see him with Athyn--and she keeps that vow.

But Athyn has sworn an oath too, one of love and vengeance. Taking the Low Road that only those mighty in magic may tread, she journeys to the Otherland, to find her lost lord and bring him home...

"A splendid tale."
--Publishers Weekly