Winds of Fury — Mercedes Lackey

VALDEMAR
is once again in peril, threatened by Ancar of Hardorn, who has long sought to seize control of the kingdom by any means at his command.

Yet this time Ancar may well achieve his goal, for by harnessing the power of Mornelithe Falconsbone, the Dark Adept, he has set into motion a magical strike against Voldemor the like of which hasn't been attempted in more than five hundred years--not since Vanyel, the last Herald-Mage, shielded the kingdom from attack by the deadliest of sorceries.

And with Voldemar's ancient spell-generated protections finally breaking down, Queen Selenoy, Herald-Princess Elspeth, and their people could soon be left defenseless against on enemy aimed with spells no one in Valdemar has the knowledge to withstand.

But as the long dormant magic of Valdemar begins to awoken, Elspeth finds that she too has a mysterious ally -- a powerful spirit from the long-forgotten past....