Arrow's Fall (Heralds of Valdemar, #3)

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.