When a mysterious beam of light starts disrupting and destroying the Earth's atmosphere, Flash Gordon (Buster Crabbe), Dr. Zarkov (Frank Shannon), and Dale Arden (Jean Rogers) - accidentally accompanied by wisecracking reporter Happy Hapgood (Donald Kerr (actor)) - swing into action in Zarkov's rocketship, believing that it could be coming from the planet Mongo. Once in space, however, they discover that the ray is originating from Mars.