Stonecaller. The Talisman Series, #2

Return to the Hidden WaysKicked out of the caravan for his gambling, Qedrim's luck has run out. Stranded in the wilderness, he uses his magical talent for slinging stones to save a strange merchant, Shapakail'esh, and is rewarded with a passage through the Hidden Ways-a mysterious and ancient method of travel. This leads him to the city of Higfrod, where he finds himself in the middle of political intrigue after saving Lady Annavristi from an assassin and winning her favor.
But his restlessness is short-lived. War soon erupts, and Qedrim is swept into the conflict, joining a merchant encampment that follows behind the army to provide supplies. When the battle turns against them, he knocks a cavalry commander from his saddle and finds himself enlisting in the army's slinger faction. To survive and protect those he cares for, Qedrim must learn to master his ability to move stones-his path to becoming a Stonecaller.
With monstrous armies led by the brutal B'tlas closing in, Qedrim's newfound power may be the key to saving Higfrod-if he can master it in time.