It's the future -- 1973 -- and a rescue team is sent to fetch Col. Edward Carruthers, the lone survivor of the first manned flight to Mars. Though he's slated for the firing squad after ostensibly murdering his entire crew, he insists that a Martian monster is to blame for the deaths. Cmdr. Van Heusen and the team doubt Carruthers' claims, until more mysterious killings occur. To their horror, they realize the bloodthirsty beast is on board the ship with them.