The Elfstones of Shannara - Terry Brooks (Book 2 of the Shannara Trilogy)

Thousands of years after the destruction of the age of man and science, new races and magic now rule the world, but an imminent danger threatens. A horde of evil Demons is beginning to escape and bring death upon the land. Only Wil Ohmsford, the last of the Shannara bloodline, has the power to guard the Elven Princess Amberle on a perilous quest to the save the world, while the leader of the Demon force aims to stop their mission at any cost.