Four astronauts get stranded on Mars. They wander around. There's more plot, but I don't like to give away the last twenty minutes of the movie.
One thing you're guaranteed of when you see the name of David L. Hewitt heavily featured on the opening credits of a movie is that the budget just might be big enough to allow you to purchase new shoelaces. And I will give him some credit; every once in a while, there is a moment that shows some imagination or captures a little of that sense of wonder. But, those moments aside, this movie mostly consists of the astronauts wandering around in caves or in the desert. When they're not doing that, they're either engaged in pseudo-scientific gobbledygook or having their ears bent by the disembodied head of John Carradine. If you're lucky, you'll wake up to enjoy the scene where they discover a Martian encased in a wall, easily the best scene in the movie. If you want to, you can speculate on the similarities between this movie and THE WIZARD OF OZ ; there's a girl named Dorothy with three companions (unfortunately, instead of a scarecrow, a tin woodsman, and a cowardly lion, she only has three bores), a yellow-brick road, and a disembodied head, and that should engage your attention for all of thirty seconds. And since we're on the subject of time, let's talk about that. The movie is seventy-eight minutes long, and it purportedly takes place over a four-day period which turns out to be only two minutes long. Those times are significant; there is about two minutes of plot here, but the movie certainly feels like four days.
And, on a side note, the original title of this movie is THE WIZARD OF MARS. My copy is called ALIEN MASSACRE. This change was accomplished by replacing the main title of the movie. Unfortunately, right before this is the credit "John Carradine as". Hence, it reads like "John Carradine as Alien Massacre", which, unlike "John Carradine as The Wizard of Mars", makes no sense. Someone obviously didn't care.