Wellspring of chaos - L. E Modesitt

Kharl is the best cooper in Brysta, one of the major cities in Nordla, and his life has been as ordered and dependable as his barrels. His trouble begins when he saves a neighbour's daughter from the violent advances of two upper-class men. Then he rescues a rape victim he finds unconscious in an alley, a blackstaffer - a young expatriate mage-from Recluce, and that makes his wife very uneasy. The culprit in both cases turns out to have been Egen, the cruel and corrupt son of the local ruler. When the blackstaffer is mysteriously murdered in Kharl's cooperage, Kharl is jailed, tried, and flogged, and in a shocking turnaround, released-and his consort executed for the murder, which she did not commit. Egen again. Kharl ends up on the run, with just a handful of coins and a few clothes, but he also takes the slain woman's black staff and her book, The Basis of Order, which explains the principles of its power. The diligent cooper is about to learn a new, very different skill.