Tom Swift's father has been working diligently on a secret project, a submarine. Tom reads in a newspaper that a ship sank off the coast during a storm, taking down with it the sum of $300,000 in gold bullion. Tom persuades his father to pursue this treasure but there is a rivalry for the treasure as another submarine soon sets off to follow Tom and his crew after they embark on their journey. But Tom knows that the other sub and its crew is not certain of the location of the wreck, and is merely following them, hoping to steal the treasure!