Joan Lowell travels by sea with her father, Nicholas Wagner, as the captain, and two additional crew, William Sawyer and Otto Siegler. During their voyage, their ship is damaged in a hurricane, her mast broken. Coming upon the wrecks of other ships, they find a mast that they can use to replace their broken one. As the two crewmembers begin salvaging the map, Lowell and Wagner explore other wrecks, where Lowell comes upon an old map which supposedly leads to ruins in the jungle which contain a precious emerald.