Brothers Bill and Gordon Hunniwell are quietly vacationing in Maine when Secret Service operative Steve Rogers arrives with a century-old letter. Written in 1816 by an ancestor, the document contains a map pointing to a hidden cache of platinum worth a fortune on the Hawaiian island of Molokai. Eager for adventure, the boys and Rogers board the Albatross, their experimental electric-motored aircraft, and embark on a daring cross-country and trans-Pacific flight.
Arriving in the islands, the trio sets up camp near the rugged cliffs of Laau Point to search for the mysterious cave marked on the brittle map. Almost immediately, they encounter hidden adversaries, including a desperate man who tries to steal their vital power cells and attempts to halt their search with falling rocks. Despite these dangerous interruptions, the boys refuse to abandon their mission and rely on quick thinking and aviation ingenuity to outmaneuver their pursuers.
Amidst their treasure hunting, the group takes a detour to Honolulu, where they assist a falsely accused resident in clearing his name and rescuing a stranded female aviator whose plane has crashed into the ocean. These dynamic encounters test their resourcefulness and courage far from home. Returning to the cliffs, they finally locate the sealed rock face indicated by the map, using dynamite to breach a hidden chamber.
Inside the concealed space, they discover a weathered wooden box containing the unrefined platinum. Just as their mission triumphs, hostile pursuers attack their campsite under the cover of darkness. The boys execute a frantic, split-second takeoff under fire, successfully escaping into the night sky with the priceless cargo.
Returning safely to the mainland, Rogers and the brothers have the metal assayed and successfully sell it to a prominent firm for a substantial sum. With their pockets full and their reputation for daring exploits firmly established, the Hunniwell boys fly the Albatross back to Maine, concluding a remarkable summer of exploration.
