The Swordsman's Oath — Juliet E. McKenna

SWORDMASTER...
Ryshad was a warrior, a sworn man pledged to defend the Empire and his lord with his sword and his life. Livak was a thief, a woman as dangerous and cunning as she was beautiful. Brought together by fate--and the wily wizard Shiv--these unlikely allies once traveled to the frozen lands of the North to find answers to an ancient mystery. Instead, though, they discovered death and worse at the hands of the Elietimm, a band of evil sorcerers who nearly destroyed them.

OR SLAVE?
Now, the Elietimm have infiltrated the Empire using their strange and deadly power. It is up to a reunited Ryshad and Livak, joined by Shiv, to discover the secret knowledge that can save the Empire--a mission that will lead them far from the lands they know. It is Ryshad, though, who will journey farthest, to a distant country where nothing is what it seems, not even the magical sword that has long protected him. And if that sword should turn against him now...