Brave explorers led by the last Druid, Walker Boh, travel across unknown seas in search of an elusive magic. However, it seems that Walker and his team were lured there for sinister, unforeseen purposes.

As the crew aboard the airship Jerle Shannara is attacked by evil forces, the Druid's protégé, Bek Rowe, and his companions are pursued by the mysterious Ilse Witch. Meanwhile, Walker finds himself alone, caught in a dark maze beneath the ruined city of Castledown, stalked by a hungry, unseen enemy.

This enemy, known as Antrax, is alive but not human. It covets the magic of Druids, elves, and even the Ilse Witch. It hunts men for its own designs, feeding off enchantment and trapping the souls of men. The fate of the Four Lands hangs in the balance.