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When industrial scientist Dr. Bryant asks Kent Fowler, the owner of an aerial patrol service, to investigate an unidentified flying object in the restricted flying area over his plant, Kent shoots down the craft. Bryant goes to the wreckage site where he meets Mota, a pilot from Mars who offers him atomic weapons secrets in trade for helping Martians take control of Earth. Needing to secure uranium for the weapons' development, Bryant sends his henchmen, Drake and Ryan, to steal it, but Kent, with the help of his secretary Helen and assistant Steve, repeatedly thwarts their attempts without discovering Bryant's true involvement. Meanwhile, Bryant relays other necessary supplies to Mota's hideout, which is in a dormant volcano, using a semi-disc plane of Martian design. When Kent investigates the uranium theft from the nearby Argosy plant and suspects Bryant is involved, the scientist orders his henchmen to place a time bomb in Kent's plane, but Helen learns about the bomb and warns Kent just in time for him to jump from the plane. Later, Mota attempts to demonstrate Martian might to government officials by dropping an atomic warhead on a bridge, but Kent crashes into the weapon to stop it, parachuting from his plane only seconds before the explosion. Just as Kent is about to secure evidence against Bryant, the scientist escapes with his henchmen but is forced to leave weapons plans behind. Bryant then abducts Helen in an attempt to trade her for the papers and sends the semi-disc plane to pick up the plans, but Kent holds the plane's pilot Trent at gunpoint and returns with him to the hideout. During the ensuing fistfight between Kent, Bryant and Mota, bombs knocked into the molten lava explode, causing the volcano to erupt and destroy the laboratory, just as Kent escapes with Helen.