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Four enterprising air cadets are suspected of a series of murders actually committed by The Black Hangman, a mysterious Nazi agent. A typical war-time serial, this Universal offering basically wasted the talents of one of the best screen villains in Hollywood history, the demonic-looking Eduardo Cianelli. Cianelli plays Karl Von Heiger, alias The Black Hangman, who has discovered a lost helium deposit in Darkest Africa. To safeguard the location, Von Heiger and mining engineer Arthur Galt (Robert Armstrong) kill the members of an expedition except for Professor Mason (Selmer Jackson) and his lovely daughter Andre (Jennifer Holt), whom they imprison. To clear their names, the four cadets -- Danny Collins (Johnny Downs), Jinx Roberts (Bobby Jordan), Scrapper MacKay (Ward Wood), and Zombie Parker (Billy Benedict) -- go in search for the villains, rescuing Mason & daughter along the way. By the 13th and final chapter, "The Toll of Treason," the boys have more or less singlehandedly wiped out the Nazi presence in Africa. Top-billed Johnny Downs, a former child actor, was better known for a series of lightweight campus comedies. Leading lady Jennifer Holt was the daughter of veteran action star Jack Holt and sister of Tim Holt. She spent most of her screen career in B-Westerns.