The Last Swordmage - a fantasy novel by Martin F. Hengst

http://www.amazon.com/dp/B00AR187RA

As far as bad luck goes, Tiadaria's has been the stuff of legend. After being sold into slavery by her father and accused of a murder she didn't commit, she finds herself facing the executioner. The only thing standing between her neck and the sharp edge of the axe is the village Constable.

After thirty years of loyal service to the Imperium, Royce has retired to King's Reach as the village's Constable. He thought that the frontier town would be the perfect place to rest, relax, and die in peace. He was wrong. With a crooked Magistrate on one hand and a conniving slaver on the other, things are anything but peaceful. To complicate his life even further, the slave with her neck on the block seems to possess the same magic Royce has hidden all his life.

Paying off Tiadaria's bond, Royce takes possession of a slave in a land where slavery is verboten. Now he must teach her to trust him, teach her to fight, and teach her about her unique abilities before they both run out of time. An ancient menace is coming. The Xarundi have returned. They are the most dangerous enemy humanity has ever faced, and they have a thousand years of bloodthirsty vengeance to exact.