A sea lab researching the ocean's potential as a new human environment is dangerously balanced on the edge of a deep sea floor trench in director Daniel Petrie's visually stunning science-fiction undersea adventure. The lab and two of its scientists are plunged into the murky depths of the abyss when a violent quake rips the structure from its moorings. A daring crew, helmed by divers, including chief diver Don Mackay (Ernest Borgnine), Bob Cousins (Donnelly Rhodes), and scientist Dr. Leah Jansen (Yvette Mimieux), sets out to rescue the victims in the Neptune, a specially designed U.S. Navy submersible able to withstand the deep sea pressures. Piloted by arrogant Navy commander Blake (Ben Gazzara), the crew of the Neptune have no idea what they are up against as they journey deep into unchartered territory, encountering many fantastical deep-sea creatures never before seen by the human eye. This futuristic exploration of the ocean floor is reminiscent of the underwater odyssey classic VOYAGE TO THE BOTTOM OF THE SEA, and features Walter Pidgeon, who appears here as Dr. Andrews, the director of the experimental project.