he discovery of a hidden cave by geologist Bradley James deeply affects him emotionally and leads a family of four intellectuals into a life-changing adventure. A seemingly accidental meeting with a beautiful girl takes them to her mysterious home constructed under the sea. The people there have adapted physically to living a life totally dependent upon the ocean, possessing astonishing ways of living and communicating underwater. without the family's specialist help, they face extinction from both a polluted environment and criminals prepared to kill them for their precious blue sapphires.