Arrow's Fall — Mercedes Lackey

VALDEMAR'S PERIL!
With Elspeth, the heir to the throne of Valdemar, come of marriageable age, Talia, the Queen's Own Herald returns to court to find Queen and heir beset by diplomatic intrigue as various forces vie for control of Elspeth's future.

But just as Talia is about to uncover the traitor behind all these intrigues, she is sent off on a mission to the neighboring kingdom, chosen by the Queen to investigate the worth of a marriage proposal from Prince Ancar. And to her horror, Talia soon discovers there is far more going on at Prince Ancar's court than just preparation for a hoped-for wedding. For a different magic than that of the Heralds is loose in Ancar's realm -- an evil and ancient sorcery that may destroy all of Valdemar unless Talia can send warning to her Queen in time!