Crown Duel — Sherwood Smith

Young Countess Meliara swears to her dying father that she and her brother will defend their people from the growing greed of the king. That promise leads them into a war for which they are ill-prepared, which threatens the very people they are trying to protect. But war is simple compared to what follows, in peacetime. Meliara is summoned to live at the royal palace, where friends and enemies look alike, and intrigue fills the dance halls and the drawing rooms. If she is to survive, Meliara must learn a whole new way of fighting-with wits and words and secret alliances.

In war, at least, she knew in whom she could trust. Now she can trust no one.