The luscious Linda Stirling starred in this 15-chapter action serial from genre specialist Republic Pictures as Claire Forrest, the daughter of that eminent inventor of the Radiatomic Power Transmitter, Dr. William Forrest (Taylor Forrest). The good doctor has disappeared during an expedition, however, and Claire asks noted criminologist Lance Reardon (Richard Bailey) for help in locating him. As it turns out, an insane scientist (Roy Barcroft), who can transform himself into the fiendish Captain Mephisto, has abducted Dr. Forrest, keeping him for ransom on his inhospitable Mystery Island. Republic threw everything but the kitchen sink into this adventure serial, which benefitted from special effects by the Lydecker brothers, Howard and Theodore; stunt work by Yakima Canutt (who is also credited as co-director), and a cast well-versed in the kind of melodramatic theatrics deemed necessary for this kind of juvenile fare. Manhunt on Mystery Island was also released in a feature version entitled Captain Mephisto and the Transformation Machine.