In the spring of 1943, Tony Del Plato gets a surprising assignment when Paramount Pictures decides to make one of its Popular Science movie shorts about inventor John Hays Hammond, Jr. Filming will take place not only at Hammond's grandiose castle-home in Gloucester, Massachusetts, but also aboard his yacht on a trip to the Caribbean. Tony's job: bodyguard to actress Marjorie Reynolds, who suggested the movie and will be featured in it.

Throughout the course of the novel, Tony reveals some of his mysterious background through a trio of stories about his tutoring by Thomas Edison, his solving of an actual New Jersey cold case from the 1880's, and his association with notorious New Jersey gangster Abner "Longy" Zwillman. But those stories aside, filming on location also manages to embroil Tony and Marjorie in a Caribbean murder.