After a deadly ray from Mars disrupts the earth's atmosphere, scientists Flash Gordon (Buster Crabbe) and Dr. Zarkov (Frank Shannon) take a rocket ship to Mars along with Dale Arden (Jean Rogers) -- and a stowaway reporter. In the Valley of Desolation, Flash and his friends are confronted by evil Emperor Ming (Charles Middleton) as they seek to destroy the deadly ray. The group is pursued to a cave, where they discover the long-suffering native Clay People, who help them in their quest.