Orissa Kane, the heroine of The Flying Girl, is a famous aeronaut in the sequel. She is piloting her brother's newly-designed Hydro-Aircraft for a demonstration in San Diego; she and her companion Sybil Cumberford fly out over the Pacific Ocean but encounter mechanical problems. The two young women land on an unknown island off the coast of Mexico, and must cope with the challenges of being castaways.
Orissa's brother Stephen, along with Sybil's father and other friends, come searching for the "air-maids" in a private yacht; but their vessel is grounded on the same island where the girls have landed. A nearby island is occupied by Mexican bandits; the encounter between the two groups leads to further excitement and complication before the Americans emerge triumphant.
In the supporting character of Sybil Cumberford, Baum creates a distinctive personality type — a person who blossoms only under adversity, and even seems to welcome danger, difficulty, and distress. Sybil is a more realistic version of Nerle in The Enchanted Island of Yew.
The Flying Girl books were intended as the start of a multi-volume series, like Baum's Aunt Jane's Nieces series that was also issued under the Van Dyne pseudonym. The Flying Girl series was not as popular as that earlier project, however, and was discontinued after the first two books. A projected third volume in the series, The Flying Girl's Brave Venture, exists only as a title in the extant records of Baum and his publisher.
The title of the second book was a matter of some debate between the author and publisher. Several alternatives were considered: The Flying Girl's Exploits and The Flying Girl's Runaway Aeroplane, The Flying Girl's Best Record and The Flying Girl on Castaway Island.