The Hardy Boys meet up with a professional diver by the name of Roland Perry, who is employed by the Crux Brothers diving company. After the boys rescue Perry from a mishap on the water, they lend him one of their father's suits, and Perry heads off to his next job at nearby Bailey's Landing. But the suit happened to contain important notes for the case that the elder Hardy was working on, so he sends the boys to retrieve them. Along the way, they run afoul of two thugs, Bock and Simon.