At a military installation near Beachwood, California, as Dr. Paul Nelson oversees the takeoff of the latest information-gathering satellite, physicist Dr. Tom Anderson meets with Gen. Tomlinson and government official Platt to insist, once again, that the project be cancelled. Tom, a brilliant scientist, believes that extraterrestrial intelligence is watching carefully and is angered by Earth’s attempts to communicate with them. As usual, Tom’s warnings are dismissed as ravings. Three months later, Tom and his wife Claire invite Paul and his wife Joan over for dinner. Despite Claire’s attempts to keep the conversation light, Tom turns the subject to alien life, and later shows Paul his radio system, on which he communicates with a voice from Venus. Just then, Paul receives a phone call informing him that his satellite has vanished from radar. As Paul rushes to the installation and orders the satellite to be grounded as soon as it is found, Claire chastises Tom for alienating their friends. Tom reveals to her that the Venutian alien is coming to save Earth, and although Claire fears for her husband’s sanity, she remains supportive. As the satellite is found and brought to Earth, Tom speaks on his radio to the alien, which has boarded the satellite. When the alien steps onto Earth, all technologies around it come to a halt, including phones, planes that fall from the sky, and Paul and Joan’s car, which stalls in the desert. Tom then informs the alien which eight people it must gain control over to complete its mission, including police chief Shallot, Gen. Pattick, the mayor, Paul and Joan. The alien releases eight bat-like flying objects to inject a radio device into their prey by which the alien can issue orders. One bat chases Paul as he and Joan walk toward Tom’s house, but he fights it off with a rock and they reach the house in safety. Tom, triumphant that his mistrusted theories have finally been proved true, tries to convince Paul that the alien wants only to rescue mankind, but Paul is disgusted by Tom’s collusion. Paul takes Tom’s car, the only one working, to his house, not realizing that the alien has been listening to him on the radio, while a frightened Claire agrees to stand by Tom. Meanwhile, Brig. Gen. Pattick, bitten by the bat, places the military installment under martial law, locks the scientists inside and sends the troops to set up posts on the desert outskirts. While Paul assures Joan that a logical explanation exists for the current situation, the bitten Shallot orders the town evacuated. Paul bikes to town, where he witnesses Shallot shooting the unarmed newspaper editor, but when Shallot tries to kill Paul, the alien instructs him to release the scientist. At their home, Claire grows more dismayed upon hearing about the alien’s mind-control methods, but fails to convince Tom that his desire to save the world comes at too high a price. Meanwhile, Paul bikes to the installation, and upon determining that the general has been bitten, knocks him out and takes his jeep. Although a bat follows him, Paul chases it away with gunshots. He goes to Tom’s, where Tom explains that the alien is one of nine, each possessing a huge intellect, who need a place to live. When Paul tries to point out that the aliens, as proven by their murderous ways, want only to herd and control humans, Tom remains unmoved and later agrees with the alien that Paul must be killed. Paul goes home, and when Joan pulls a bat out to use against him, he realizes that she has been bitten, and is forced to kill her. Tom invites Paul to return to his house that night, and Claire begs Tom not to kill Paul, kissing him until he reveals the alien’s hiding place in the desert. At the same time, in the installation, the two scientists are bitten and come under the alien’s command. That night, Claire hysterically tells the alien over the radio that she is going to kill it, and, taking the shotgun Tom planned to use to kill Paul, rushes to its cave in the desert, near the troops. Paul arrives and tells Tom he killed Joan, and now must kill him, still hoping to convince Tom that the alien is controlling him by manipulating his emotions. Tom turns for the shotgun but, seeing it missing, realizes that Claire has taken it. Claire has by that time discovered the alien and shoots at it, to no avail. The shots attract the attention of Pvt. Manuel Ortiz, who races to the cave, but is too late to save Claire. Paul and Tom hear her screams over the radio, which finally persuades Tom to join Paul against the alien. They rush together to the installation, where they shoot the general and scientists, not realizing that the general has only faked his death. Shallot shoots at Tom, who grabs a blowtorch and kills him while Paul fights off Pattick. Paul and Tom race to the cave, where the soldiers are being killed en masse by the alien. Tom approaches it bravely, condemning it for its destructiveness. The alien attacks, but Tom burns out its eyes and destroys it, before dying of his wounds. As Paul sadly surveys the desolate scene remaining, he reflects that if hope exists, it resides in man himself.