A volcanic eruption in the North Atlantic brings to the surface a 65-foot prehistoric monster. Two treasure divers capture the creature and take him to London where he made the star attraction at a circus. A scientist is thoughtful enough to point out that the sailors' bonanza is only an infant, and that a full-grown specimen would be over 200 feet in height. Sure enough, Gorgo's mama comes thundering ashore, reclaims her offspring and heads back to sea - but not before, she trashes a generous portion of London.