When adventurer Bowen Tyler is taken aboard an enemy submarine, he never dreams that his voyage will end in a land where time itself is prisoner. But in the uncharted seas at the bottom of the world, Tyler and the crew of the U-33 discover the mysterious forgotten continent of Caspak, where the savage denizens of a thousand lost ages roam vast primeval jungles. Surrounded by dinosaurs and Bronze Age warriors, saber-toothed tigers and cunning beast-men, Bowen Tyler begins to unravel the incredible secret of Caspak, even as he battles to save the life of the woman he loves.