A lush, tropical, verdant paradise in the South Pole? Living dinosaurs? Such fanciful ideas must surely be the ravings of a madman. Or perhaps not, as Admiral Nelson soon discovers. The question is, will he and Crane survive their trip to a lost world?

A Soviet satellite has crashed into the sea and its nuclear reactor must be disarmed before it causes a disaster. Two Soviet scientists come aboard Seaview to carry out the work -- but one of them is an imposter.