The Shannara series. The Elfstones Of Shannara. Book 2

Ancient, ultimate evil threatened the Elves and the Races of Man. For the Ellcrys, the tree of long-lost Elven magic, was dying, loosing the spell of Forbidding that locked the hordes of Demons away from Earth. Already the fearsome Reaper was free. Only one source had the power to stop it: the Elfstones of Shannara. And the valiant companions must ride again in an impossible quest to find them.