A group of five boys known as the Rambler Club, joined by Cranny Beaumont and his guardian's ward Willie Sloan, travel to Wyoming and find Border City amid a Western boom. Encounters at Circle T Ranch and with a financier experimenting with a dirigible balloon lead the club to acquire an aeroplane and embark on a sequence of airborne and frontier adventures. Willie's puzzling temperament and occasional courage shape several surprising episodes while Bob Somers's cool skill as an aviator is repeatedly tested. Events include flights and aerial rescues, dealings with herds, an underground passage, capture and escape, and a final over‑mountain journey.