The Talismans Of Shannara: The Heritage of Shannara, book 4

The descendants of the Elven house of Shannara have all completed their quests: Paranor, the Druid’s Keep, has been restored; the Elves have been returned to the Four Lands; and Par Ohmsford has found what he believes to be the legendary Sword of Shannara. But their work is not yet done. The Shadowen still swarm over the Four Lands, poisoning all with their dark magic, and their leader is determined to prevent the scions of Shannara from sharing the knowledge that will end the sickness. To this end he sets his traps. For Walker, he will dispatch the Four Horsemen; for Wren, he sends an untrue friend; and for Par, he devises the most terrible fate of all…The charges given by the shade of the Druid Allanon seem doomed to failure - unless the Shannara children can escape the traps being laid for them, and Par can unlock the secret of the Sword of Shannara.