The Jetmarine, the second great invention of Tom Swift Jr., takes the young inventor into a desperate battle with bold modern pirates who have been ravaging the sea lanes off our southern coast. The atom-powered, two-man submarine is launched just in time for Tom and his pal Bud to set out to rescue Tom's father, who has fallen into the hands of the pirates. The wily enemy pulls no punches in trying to wreck the amazing Jetmarine that outspeeds any sub and is able to plunge miles to the ocean floor.