Antrax

In his last novel, Ilse Witch, a brave company of explorers led by the last Druid, Walker Boh, traveled across unknown seas in search of an elusive magic. Yet perhaps Walker and his team were lured there for sinister, unforeseen purposes.
Now in Antrax, as the crew aboard the airship Jerle Shannara is attacked by evil forces, the Druid's protege, Bek Rowe, and his companions are 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.
For there is something alive in Castledown. Something not human. Something old beyond reckoning that covets the magic of Druids, elves, even the Ilse Witch. Something that hunts men for its own designs: Antrax. It is a spirit that commands ancient technologies and mechanical monsters, feeds off enchantment, and traps the souls of men.
With the Jerle Shannara under siege and Antrax threatening the bold and unwary, the Ilse Witch finds herself face-to-face with a boy who claims to be the brother she last saw as an infant. Now a young man, Bek wields the magic of the wishsong and carries the Sword of Shannara upon his back. Unsure whether to trust Bek or to slay him, the Ilse Witch takes him prisoner. One has come pursuing truth, the other revenge. Yet both seek Walker Boh - with the fate of the Four Lands hanging in the balance.