Wings Of Wrath: The Magister Trilogy: Book Two by Celia Friedman
In a world where the price of magic is life itself, a group of seemingly immortal sorcerers appear to have cheated the system.
And now Kamala has breached their secrets, she seeks to join their ranks as the first female Magister. But they would rather see her dead, forcing her to flee to the frozen north. There Kamala will find an evil far greater than a sorcerer's enmity, and will hear a dire prediction of a future war.
In a past age, an ancient bloodline was cultivated to stand in the path of darkness. Now its warriors must unearth the truth at the heart of the legends, and stand firm against an enemy that brought mankind to the very edge of destruction. And Kamala must join their battle.