The first manned spaceship to Mars crashes. When a rescue ship is sent to find out what happened they find only one survivor, but on the way back to earth they discover that they have on board an alien intent on killing them. Whilst it is possible to find lots of holes in the science, after all it was made in the 1950's, it is still a passable thriller set in outerspace.The was reputed to be the inspiration for the RIpley character in Aliens.