Exile’s Honor (Valdemar, 1)

The national best-selling novels of Valdemar are among the most beloved and acclaimed works of Mercedes Lackey's career. This brand-new, stand-alone book in the series tells the story of one of Valdemar's most popular continuing characters-the prickly weapons-master Alberich.
He was once a Captain in the Army of Karse, a kingdom which has been at war with Valdemar for decades. But when Alberich took a stand for what he believes in-and defected-he was chosen by one of the magical Companion horses...to serve the queen of Valdemar.