Flying students Danny Collins, Jinx Roberts, Scrapper McKay and Zombie Parker are suspected of a series of murders perpetrated by a Nazi agent known as the Black Hangman. The latter is an engineer, Arthur Galt, who has disposed of several people who accompanied him on an expedition which located lost helium deposits in Africa. Galt has also imprisoned the remaining members of the expedition, Professor Mason and his daughter Andre. Galt plans to sell the helium to Germany through a Gestapo ring headed by Kurt von Heiger. The four cadets, thinking Galt is their friend, fly with him to Africa as they hope to track down Von Heiger, thinking he is the Black Hangman, and clear their own names of the murder charges. They are pursued to Africa by U.S. Army Intelligence officer Captain Ralph Carson.