In this race-against-time disaster thriller, Charlton Heston is Captain Paul Blanchard, stuck sixty miles off the Connecticut coastline on the edge of an ocean canyon in a nuclear submarine. If he and his crew are not rescued immediately, disastrous consequences will be had by all. As the time slips by, Blanchard must instill courage into his nervous crew -- while his second in command, Commander Samuelson (Ronny Cox), cracks under the pressure. But help is on the way as Captain Bennett (Stacy Keach) races to the rescue. All is going well until an earthquake tremor causes the submarine's escape hatch to be buried under the sea. Then Captain Gates (David Carradine) and his assistant Mickey (Ned Beatty) arrive with their experimental diving vessel called the Snark. Now it is up to them to try to save the crew of the submarine, but no one knows if the Snark will function properly or not.