The elfstones of Shannara #2 Book 2 of the Shannara series

Ancient Evil threatens the Elves: The ancient tree created by long-lost Elven magic, is dying. When Wil Ohmsford is summoned to guard the Amberle on a perilous quest to gather a new seed for a new tree, he is faced with the Reaper, the most fearsome of all Demons. And Wil is without power to control them....From the Paperback edition. 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 the Elfstones of Shannara could stop it The second book in the classic Shannara series.