The Voyage of the Jerle Shannara by Terry Brooks (#2)

Brave explorers led by the last Druid, Walker Boh, traveled across unknown seas in search of an elusive magic. But now it seems that Walker and his team were lured there for sinister, unforeseen purposes. As the crew aboard the airship Jerle Shannara is being attacked by evil forces, the Druid's protege, Bek Rowe, and his companions are being pursued by the mysterious Ilse Witch. Meanwhile, Walker is alone, caught in a dark maze beneath the ruined city of Castledown, stalked by a hungry, unseen enemy. It is alive, but not human, coveting the magic of Druids, elves, even the Ilse Witch. It hunts men for its own designs. It is Antrax: a spirit that feeds off enchantment and traps the souls of men. And with it, the fate of the Four Lands hangs in the balance.