Universal's 16th sound-era serial (following "The Jungle Mystery" and preceding "Clancy of the Mounted", both starring Tom Tyler) was based on Sir Arthur Conan Doyle's short story (loosely adapted), and opens with a special train carrying gold bullion from the Golconda Mine, that is stopped by henchmen, working secretly for Sam Slater (J. Frank Glendon), partner of Potter Hood (Francis Ford), in the mine ownership. Laying down portable tracks, the bandits take the train off of the main line, hide it in an abandoned mine shaft, steal the gold, and pick up their make-shift tracks, leaving a mystery in their wake. Potter's son Tom Hood (Frank Albertson), just home from college, determines to solve the mystery with the aid of his pal Bob Collins (football great Ernie Nevers.) They board the gold-shipment special train on its next run.