Plot

An evil alien brain from the planet Arous hijacks the body of an Earth scientist in order to control the Earth.

Gor, a powerful criminal brain from the planet Arous, assumes the body of scientist Steve March. Through March, he begins to control the world by threatening destruction to any country challenging his domination. Another brain, Val, works with March's future wife Sally to defeat Gor. Val explains that Gor will be vulnerable when he is forced to leave March at intervals to re-energize. Gor's vulnerable spot, the Fissure of Orlando, is described in a note left by Sally in Steve's lab.—Apostrophes

Titles and credits run over a vista of the desert with a mountain in the background. It is evening and a light descends from the sky and explodes into the mountain. Dr. Steve March (John Agar) is in his lab working and notices something strange on his Geiger counter. He tells his colleague, Dan Murphy (Robert Fuller) that it makes no sense. Dan is absorbed reading a pulp science fiction novel and is paying no attention, until he hears the Geiger counter suddenly register radioactivity after a long silence. Steve has located the source. It is thirty miles away at Mystery Mountain. Sally Fallon (Joyce Meadows) arrives and reminds her fiancé and Dan that they haven't even stopped for lunch. After another burst of radioactivity is detected, Steve proclaims, "Dan, were going over to Mystery Mountain." Sally convinces them they need to eat first.

At the Fallon residence they have lunch. John Fallon (Thomas Browne Henry) arrives home. He is Sally's father. Steve explains that he and Dan are going to Mystery Mountain. John is surprised. He explains that at this time of year temperatures can reach 120 degrees in the desert. Steve reveals that, "A hot blast of gamma is coming from Mystery Mountain. That's cause enough for any scientist to go out into the desert." Dan is not anxious to go, but agrees. They set out in a Jeep. A rock fall blocks their path. Steve notices rock debris indicating recent activity, and they walk the rest of the way. They make their way to a cave. Steve is convinced it was blasted out recently, but notices no footprints. With flashlights in hand, they walk through the cave checking their counters for any radioactivity. Suddenly the counter registers a high dose of radioactivity, then just as suddenly goes silent. They pull their weapons and announce themselves. They see it--a bright light followed by the floating apparition of a huge brain with glowing eyes. Steve empties his gun into the form and collapses. Dan fires a couple of rounds from his rifle and also succumbs to the bright light emanating from the creature. It is an intense burst of radiation that kills him. The brain shrinks in size and enters Steve's body.

Sally is at home, out on the porch with her dog, George, when the phone rings. It is her father inquiring about Steve and Dan. Steve appears outside, enters the house and embraces Sally. He tells her they found nothing. He is uncharacteristically aggressive and she is slightly taken aback. She asks about Dan and is told he went to Las Vegas. Sally is suspicious and notices something is different about her fiancé. Steve winces in pain, then recovers explaining it is just a toothache. He kisses her again, even more aggressively, tearing her blouse. George comes to her rescue attacking Steve. Steve fights off the dog, then storms off. He gets in his car and drives away. Back in his lab, Steve is seated in a chair when the brain exits his body. The brain tells Steve, "I am Gor. I need your body as a dwelling place while Im here on your Earth." Gor explains that Steve was chosen specifically because of his special knowledge of nuclear energy and his access to government facilities.

John Fallon returns home and greets his daughter. Sally tells her father she thinks Steve is ill. She suspects that something is wrong. John stops by Steve's lab to talk to him. Steve has another attack and asks John to leave. When he stands up from behind the water cooler we can see his metallic eyes. At the Fallon home, John and Sally have lunch. Sally continues to express her concern about Steve. She convinces her father to make a trip out to Mystery Mountain the next morning. They take the same route and stop at the rock fall. There they find the canteen and jeep tracks left by Steve and Dan. They walk down to the cave to rest. Sally remarks that the cave is new. They explore the cave system and find Steve and Dan's footprints. Sally notices a flash of light and screams. They walk on and find Steve's abandoned scintillator. John's light reveals Dan's body. He walks over and notices the burns on the body. Vol, another brain from the planet Arous, appears and communicates with John and Sally telepathically. He explains his mission on Earth. He is here to capture or kill the criminal, Gor. He closes his encounter with John and Sally with a promise to meet them at their home at 8:00 p.m. the next evening.

Steve makes a call to the Atomic Energy Facility at Indian Springs. He invites himself to the next scheduled test on Friday, as an observer. Gor plans a test of his power that day. He promises Steve power and wealth. At the Fallon home, right on time, Vol appears. He invites the Fallons to help him save the Earth. He asks for a host that can get close to Gor while he inhabits Steve's body. They settle on George, the dog, as a host for Vol. Vol enters the dog. Gor re-inhabits Steve's body. Steve finishes dressing and drives to the Fallon home. On the way he sees an airplane in the sky. He stops and with his metallic eyes destroys the airliner mid-flight. He laughs then continues his way to see his fiancée. Vol, now safely hidden in George's canine body, joins Sally and Steve in the car. They stop and talk. Steve promises Sally the world, then roughly kisses her. He hints at a new power that, "Will make me the most feared man on Earth." A radio broadcast they hear in the car about the airplane crash diverts them to the scene. The Colonel in charge shows Steve one of the bodies. He is burned like Dan Murphy. He escorts Steve over to meet Professor Dale Tate (Dale Tate). They examine a piece of wreckage and note the radiation damage. Steve and Sally talk about the power that destroyed the plane. When she gets home she tells her father about the plane crash. Vol tells father and daughter that Gor can only be destroyed when he assumes his true form. While he is in transition or occupying Steve's body his is invulnerable. "In Earth's atmosphere, we must return to our true state once every twenty-four hours in order to assimilate enough oxygen for life." He further reveals that a heavy blow on a region known as the Fissure of Rolando can kill him.

Sheriff Wiley Pane (Tim Graham) comes to see Steve at his lab. He wants to ask Steve a few questions about Dan Murphy. He tells Steve that Dan is dead. Steve sticks to his Las Vegas story, but the Sheriff explains that he knows when and how Dan died. When pressed, a confidently possessed Steve confesses to the murder of Dan and the destruction of the airliner. He quietly tells the sheriff, "And now I'm going to kill you." The Sheriff pulls his gun, but is stopped by a bright flash of light. Steve stashes his body in the corner of the lab.

At the Pentagon, a military committee assembles to examine the wreckage and concludes the Earth has been invaded. The Colonel chairing the committee, later specifically addressed as Frogley by Steve, (Ken Terrell) reports that Dan and the passengers of the airplane were killed by intense radiation. The group adjourns and plans to meet again at Indian Springs. Steve and the dog arrive at the Fallon home. Steve explains that the dog stopped by the evening before and stayed to eat. Vol never had a chance to confront Gor, as he never left Steve's body. Steve gloats about the upcoming meeting at Indian Springs. He promises Sally fame and fortune when they move to Washington, D.C. She pretends to love Steve, so as not to make Gor suspicious.

Steve appears at Indian Springs for the Friday test. He is introduced to General Brown (E. Leslie Thomas). Steve explains that he has an explanation for the deaths of Dan and the aircraft destruction. Steve walks over to the window and invites the assembled to watch the closed circuit television. He unleashes a power that destroys all the targets set up for the planned nuclear test. He calmly tells the group, "What you've just seen me do to that one small area, I can do to a city, a nation, or a continent." The Colonel (addressed as Frogley by Steve) leaves the room. He returns with a gun and empties eight bullets into Steve with no effect. A flash of light dispatches the Colonel. Steve orders that representatives of the superpower nations return to discuss terms. Any nation that does not attend will have their capital city destroyed.

Steve meets with the superpower representatives. He chastises the Russian representative (Bill Giorgio) for his late arrival. General Brown explains to the representatives that Steve is not joking. He has seen first-hand the death and destruction the man caused. The man is to be taken seriously. They walk over to the window and watch as Steve destroys another airliner. Steve laughs maniacally and resumes his meeting. He demands all the Uranium and Plutonium available on Earth. In addition he insists all atomic resources, factories, transportation and shipping, industrial facilities be put at his disposal for the purpose of building an invasion force. He will use an interplanetary force, the Earth will supply, to invade Arous. He closes the meeting.

Sally surreptitiously enters Steve's lab. She makes a note on a page with a diagram of a brain of Gor's vulnerable spot. She leaves the page on a table next to his chair. As she is about to exit the lab, Steve arrives. She hides herself as Steve falls into his chair and Gor exits his body. Sally does not see the Sheriff's body, yet. While Gor proudly boasts about his accomplishments, Steve sees Sally's note and an axe by the fireplace. Sally finally sees the Sheriff's burned body and screams. This diverts Gors attention towards her, leaving Steve time to grab the axe and hit Gor while he is in a solidly physical state. He strikes the vulnerable Fissure of Rolando region on Gor and kills him. Seeing his enemy vanquished, Vol exits George's body and departs the area. Sally tells Steve about Vol and how she knew how to kill him. She brings George into the lab and talks to him, as she thinks Vol is still using George as a host. When the dog does not respond she is perplexed. Steve doesn't believe her story telling her, "You and your imagination." They embrace and kiss. We close with the opening shot of Mystery Mountain.