Empire of night / Kelley Armstrong.

Two sisters. An empire on the brink of war. And a ruthless traitor prepared to unleash hell upon the world...Moria and Ashyn have lost everything except each other. Betrayed, orphaned and kept under close guard at court, they are desperate to find help for the children of their village, kidnapped by a terrifying enemy. But their quest is tangled in a much greater battle - for the fate of the empire itself. Torn apart by violence and intrigue, the sisters will learn a great deal about their powers and their potential. But they will also learn the heartbreak of betrayal and loss, as those they love reveal their dark secrets.