Frederick Fielding secretly marries his neighbor, Marguerite Quinn, and gives her his signet ring, even though her mother and father are enemies of his parents. The young groom then travels to the coral-rich island of Crimson Shoals, which is owned by his father, Thomas. Years later, Frederick, a prosperous owner of the island, grieves upon learning his wife has died, but is soon preoccupied with the theft of its coral reserves. Suspecting foreman Jack Quinn, Frederick and Thomas sail for the island. Helen, a member of Frederick's crew, falls in love with Jack and discovers that Rex Burke, the company auditor, is responsible for the theft. After a series of adventures and fights, Jack drops a charge of dynamite from an airplane, destroying the submarine Rex used to steal the coral. Frederick notices that Jack is wearing Marguerite's signet ring, and realizes that they are father and son, enabling Jack and Helen to continue their romance.
—AFI