Plot

On the last day of their mission to Mars, three astronauts - Ed Barkley, Alan Wells and Pete Claridge - discover a cave with hieroglyphics on one wall. They also find a pod-like object but they are knocked out after trying to move it. They make it back to their ship and begin their voyage home. Five months into that return trip they begin to have equipment malfunctions and find a small growth of alien origin. Soon, one of the astronauts begins to believe that the others are aliens who have taken over the bodies of his shipmates.—garykmcd

Three astronauts exploring Mars discover a mysterious canister. When they open it, they are struck unconscious. Awakening nearly an hour later, they must hurry back to their ship to make their launch window. But on the way home, Ed becomes convinced that fellow astronaut Alan is not what he appears to be, and murders him by forcing him out the airlock. Now Ed and his remaining crew member Pete must decide what to do.—CommanderBalok