Legacy Of Kings: The Magister Trilogy: Book Three by Celia Friedman
THE WORLD PREPARES FOR WAR - AND THE END OF DAYS DRAWS NEAR
An ancient enemy has returned to the human kingdoms. These creatures prey on the souls of men - and if both magic and might fail to defeat them, the Second Age of Kings will fall into darkness.
Magisters are marshalling their sorcerous powers to form a war alliance, but treachery is already eroding its ranks. Magister Colivar is withholding a deadly secret that links sorcerors to the Souleaters themselves.
In this time of change, Kamala may finally win acceptance as the only female sorceror. If she can locate the Souleaters' stronghold, the Magisters might lift her death sentence. Yet to do that she will have to embrace an alien and terrifying birthright - and all the souls of men will be tested in the aftermath.