The Gathering Storm by Tricia Owens

After betraying the only man he ever loved, Hadrian ni Leyanon waits for death amid the ruins of a sorcerous battle. Before that can happen, he is recruited by the Council of Elders, which governs the use of magick in Juxtan. The Council needs him to track down his evil sorcerer father and force him to face the justice they aren’t powerful enough to inflict on their own. Wracked with guilt, Hadrian agrees to join the mage-led mission in the hopes it will allow him to redeem himself. But when Caled, the handsome mercenary whom Hadrian betrayed, insists on joining the mission too, Hadrian discovers that redemption needs to come from the man who hates him most.
Caled has forsaken his family name to become an instrument of justice. Stalking Hadrian through the halls of the mage school where the young sorcerer is recovering, Caled is determined to see that justice comes not just to the father but to the son, even if his heart cries out for him to reconsider.