After a plane crash, two opposing half-brothers find themselves on an amazing lost island where enlightened pacifist humans and intelligent talking dinosaurs have created a utopian medieval society. But imminent disaster approaches.

Hornblower and his comrades come under the command of a revered but obviously mentally unstable captain and eventually must mutiny.

Lt. Hornblower and his crew are captured by the enemy while escorting a Duchess who has secrets of her own.