The Elfstones Of Shannara. Tome 2

The Ellcrys, the tree of long-lost Elven magic, is dying, unravelling the spell of Forbidding that locks the hordes of Demons away from the world. Already the fearsome Reaper is free. Only by quickening a new seed in the mysterious Bloodfire can the Ellcrys be reborn and the Forbidding made whole. Amberle, a young Elven girl, is chosen to undertake the quest. The way is perilous, though. Other demons besides the Reaper stalk the land.
Amberle will need a protector if she is to prevail, and Wil Ohmsford, heir to the elven magics of Shannara, is chosen to accompany her. Amberle's quest and the fate of the Four Lands will rest on Wil's ability to unlock the magic of the mysterious Elfstones of Shannara.