As head of Z5, the organization dedicated to international peace, Dr. Palfrey is deeply alarmed when Professor Corvell, an eminent scientist, is swept of an ocean cruiser by a strange, gigantic wave. The Professor is only the most recent in a long list of men who have disappeared mysteriously into the ocean - and all were highly trained people: scientists, athletes, physicians, etc.

These events suggest to Dr. Palfrey an improbable possibility, the existence of a world beneath the ocean - one that populates itself by plucking useful people off the surface!

What Palfrey doesn't know is that he is moving inexorably to a confrontation with a man determined to control not only the depths of the ocean, but the entire world as well...