A Martian invader crashes his spaceship conveniently close to the workshop of a scientist who is developing an interplanetary craft. If the extraterrestrial Purple Monster can complete the rocket ship and return to Mars, he will be able to start a full-scale invasion of Earth. Good thing Craig Foster sets out to thwart the Monster's mission!

• Republic Pictures
• Roy Barcroft
• Dennis Moore
• Linda Stirling
• James Craven
• Bud Geary
• Mary Moore
• John Davidson
• Joe Whitehead