Colonel Floyd Graham (Lloyd Bridges) heads a rocketship mission to the moon which blasts-off from Earth only to accidentally land on Mars instead. The intrepid astronauts, true to their intrepid nature, decide to explore anyway and are shocked to discover that the Red Planet once had a civilisation which was almost completely destroyed in an atomic holocaust, leaving the survivors to regress to the level of primitives. Urk! Watch out! Danger lurks in every crater!