The High Druid's blade / Terry Brooks.

Legend has it that Paxon Leah is descended from the royals and warriors who once waged war with magical weapons. But those heroes are long gone now, and there is nothing enchanted about the antique sword that hangs above Paxon's fireplace. Paxon leads a quiet life - until extraordinary circumstances overturn his simple world ...and rewrite his destiny. When his sister is abducted by a mysterious stranger, Paxon races to her rescue with the only weapon he can find. He is stunned to discover powerful magic unleashed within him - and within his ancestors' ancient blade. But his formidable new ability is dangerous in untrained hands. Paxon must master it quickly, as his near-fatal clash with a dark sorcerer won't be his last. Leaving behind home and hearth, he journeys to the keep of the Druid order to learn the secrets of magic and earn the right to become their sworn protector.