Professor Steve March (John Agar) is inspecting the instruments in his laboratory when he calls his assistant Dan Murphy (Robert Fuller) over to take a look at some unusual readings. Dan isn't entirely convinced, but Steve thinks that there are notable bursts of radiation coming from the desert, specifically Mystery Mountain, and wants to head out there as quickly as possible. Steve's fiancée Sally Fallon (Joyce Meadows) enters the room and admonishes the men for not having eaten lunch, persuading them to go outside to the barbecue she has prepared. However, it's not long before the two scientists are driving into the desert and a world-shattering terror...
Written by Ray Buffum, The Brain from Planet Arous was not the only alien possession B-movie from 1958, although its main rival, I Married a Monster From Outer Space, dealt with its horrors rather more soberly. What Steve and Dan find in the desert is a newly-blasted cave, and on venturing inside the unexpected greets them: the large, telepathic, floating brain of the title. One week later and Steve returns home with a half-baked story about Dan travelling to Las Vegas for a break from nuclear science, and Steve himself is acting strangely, and distinctly horny in his advances towards Sally whereupon he almost rapes her in the garden.
It doesn't take a nuclear scientist to work out that Steve has been possessed by the alien brain, named Gor (and voiced by associate producer Dale Tate). Agar has suffered a lot of criticism over the years for his wooden perfomances, but here he appears to relish the opportunity to play the bad guy and is surprisingly enjoyable to watch (although he wasn't too keen on the metallic contact lenses he had to wear for the role). His brain-controlled Steve is a power mad would-be tyrant who plans to - what else? - take over the world with his explosive abilities.
All is not lost as we see when Sally and her father (Thomas Browne Henry) take a trip of their own out to the cave and encounter another alien brain, this one calling itself Vol. Vol is a decent sort who tells them that Gor is giving alien brains a bad name and that he is wanted on his home planet of Arous for major crimes. Unfortunately, he can't be caught when inside Steve's body, only when he is floating out of it for a rest, and so Vol possesses the body of his dog, George, in an attempt to get nearer to him. This kind of alien criminal plotline would crop up in later films such as The Hidden, Dark Angel and Men in Black, so you could say this effort was a pioneer in its own modest way.
Gor shows his contempt for the human race by blowing up an aeroplane flying overhead one night, but he has bigger fish to fry. Steve, meanwhile, is well aware of the mayhem being caused, yet is powerless to stop it: occasionally he will grimace and double over as he tries to reassert control, but it's all in vain. Of course, this being a nineteen-fifties science fiction movie atomic energy is the main threat to be used by its villain, as if to show how dangerous it is when it gets into the wrong hands, but mostly this is an adventure in stopping the baddie before he gets his way, here by whacking him on his Fissure of Rolando (which would bring tears to anyone's eyes). Nathan Juran directs with admirable briskness (one shot of Agar through a water cooler is especially inspired) and the film is amusingly daft, with a hilarious final line. Music by Walter Greene.