A Demon in Silver (War of the Archons) by Richard Ford
In a world where magic has disappeared, rival nations vie for power in a continent devastated by war. When a young farm girl, Livia, demonstrates magical powers for the first time in a century there are many across the land that will kill to obtain her power. The Duke of Gothelm's tallymen, the blood-soaked Qeltine Brotherhood, and cynical mercenary Josten Cade: all are searching for Livia and the power she wields. But Livia finds that guardians can come from the most unlikely places... and that the old gods are returning to a world they abandoned.