The swordsman's oath - Juliet E. McKenna

Ryshad had no choice but to kill his long-time friend and ally Aiten. Aiten's mind had been corrupted by the mysterious Elietimm and he was a danger to himself and a deadly threat to others. But that is no consolation to the grieving Ryshad and certainly will be of no help when he tries to explain it to Aiten's family.

To distract him from his troubles and from the strange dreams he has been having, Ryshad's patron, Messire D'Olbriot, sends him to Caladhria to assist the wizard Shiv, who is working for the Archmage himself. The wizards are trying to find a way to combat the strange aetheric magic of the Elietimm, which threatens to destroy the land. But Ryshad's desire to help goes far beyond the patriotic - he seeks revenge for the death of Aiten. What he doesn't know yet is that he will have to work with Livak, with whom he had a brief love affair, and that the strange dreams he has been having may hold the key to the mysterious Elietimm ...