The first novella, "The Land That Time Forgot," opens after the outbreak of World War I but before the United States has entered the conflict. Bowen J. Tyler, Jr., an American, is sailing by passenger ship to France in order to join the fight against Germany. When his ship is torpedoed by a German U-boat, Tyler and the woman passenger he saves, Lys La Rue, are rescued by a British tugboat.

They and the crew soon seize control of the U-boat, which, after much shipboard intrigue, ends up near Antarctica.

Short of fuel, food, and water, the crew sights a mysterious island surrounded by high cliffs, and sails the submarine through an underground river into the fantastic world of Caspak.

All three novellas are set in Caspak, a land where evolution occurs at a rapid pace. There is a large sea in the middle of Caspak, and the...