Beverly West appeals to Harry Harper, the inventor of a submarine device for salvaging sunken vessels, to help her rescue her father from the South Sea natives who are holding him as a ransom for the skull shaped pearl that Beverly possesses. Also desirous of the pearl is Job Mourdant, Beverly's guardian, who kidnaps his ward and heads out to sea. Harry follows and saves Beverly when Mourdant throws her overboard. After the two parties arrive on the island, Harry is captured but escapes in time to see the natives thrust Beverly into an iron safe and throw her into the sea. Once again, Harry saves the girl, and finally procures the gems after struggling with a man in a diving suit. Harry then so impresses the natives with his magic that they release Beverly and her father and the three set sail for home.