More noted in its day for its underwater photography than for any distinction in its script or characters, this simple crime drama evolves around the retrieval of a priceless emerald from a sunken ship. Stuart Godfrey (John Farrow) is the black-hearted leader of a diving expedition to get the gem. He has forced the winsome Joanne (Nan Adams) to pretend to be his wife and has conned an outfit of frogmen into diving for the emerald. Dave Courtney (Jon Hall) heads up the divers, who mysteriously start to die off after one discovers an underwater skeleton with Godfrey's belt still tightly wound around its neck. The underwater mayhem continues right up to the above-water ending.