Marine scientists prepare to leave their Underwater habitat ''Oceanlab'' after an extended stay performing oceanographic research. An underwater earthquake interrupts their plans. Dr. Andrews (Walter Pidgeon) enlists experimental sub captain Adrien Blake (Ben Gazzara) to survey the damage and rescue the Aquanaut. He brings along Chief Diver "Mack" MacKay (Ernest Borgnine) and Dr. Leah Jansen (Yvette Mimieux), fiancée of one of the scientists.