After landing on Mars, the crew of an investigative spaceship sets out to explore the planet's surface. They encounter a carnivorous plant and afterwards it takes them to a stand of alien trees which is revealed to actually be the limbs of an alien forty-foot bat-rat-spider creature. The creature attacks the female lead iris but is ultimately blinded and repelled by Chief Weapons Officer Jacobs's freeze-ray gun. Upon return to their ship, the crew finds that their radio has been blocked. The ship is held by an alien force field, preventing liftoff, leaving them trapped with the bat-rat-spider.