The Keeper's Promise by Katie Sweet

The Keeper’s Promise is the story of a world on the brink of war, and the descendants of the ancient Keepers who must be gathered to defend the land once more from the incursion of the Iziiran General, Mordth. Dhel is a young Rhyjain Rider whose life is turned upside down when he is tasked to deliver an ill-fated message to the King of Whitecrest. Kaythe is the King’s daughter, headstrong and gifted with a strategic mind, but locked in a struggle with traitorous kin who would destroy everything her father has built. Kestan is the Firelord’s youngest son, born without the full powers of the True Blood, and so struggling to find a place for himself in the shadow of his brother and cousins. Orsol is an exiled Tellak prince, searching for a sign from the gods that now is the time to retake his throne.