Dr. Karol Noymann, an atomic scientist played by John Carradine, is killed in a laboratory explosion, a tragedy that sets off a chain of unsettling discoveries and growing fear. His colleague, Dr. Adam Penner, portrayed by [Philip Tonge], is deeply shaken by the disaster, resigns in protest, and calls for changes that might prevent future catastrophes.
At Noymann’s funeral, an invisible alien takes over the scientist’s dead body and begins to reveal its ominous message. The entity warns Penner that Earth must surrender or face an invasion in which the dead are inhabited and used to sow chaos. The alien demonstrates its power by making objects vanish, a display that leaves Penner, his daughter Phyllis Penner, and Dr. John Lamont—[Robert Hutton]—reevaluating everything they thought they knew. They try to warn Washington, but the government ignores the warning and the media brands Penner a crank.
Penner, accompanied by his daughter and Lamont, returns to Noymann’s grave and is confronted again by the invisible intruder. The threat multiplies: at an airplane crash site, another alien inhabits a dead pilot, then attends a hockey game and chokes the announcer, issuing the same ultimatum. A separate body—taken from a car accident—arrives at another venue, spreading fear as aliens take over more victims and unleash chaos worldwide: flames, destroyed dams, and ruined cities.
Major Bruce Jay, the military lead, arrives to escort Penner, Phyllis, and Lamont to a secret bunker. Along the way they face a frightened farmer—The Farmer, played by Hal Torey—whom the Major shoots to protect the group. Inside the bunker, the government contacts them and tasks them with stopping the invasion. They quickly deduce that the aliens are radioactive and decide to capture one for testing. An early attempt to seal an alien with acrylic fails, but they manage to trap another by filling a hole with the liquid and luring the creature into it. The captured alien is brought back to the bunker and confined in a pressure chamber, where the acrylic casing is breached by high air pressure.
The alien offers to spare them if they release it; the Major refuses. A heated argument between Lamont and Jay escalates into a collision of nerves and equipment, triggering an alarm that exposes the alien’s vulnerability to noise. They build a sound-based weapon and test it on the alien: it becomes visible and dies from the sonic assault. Attempts to contact the government are thwarted when the aliens jam the radio, but a radio direction finder leads them toward the alien ship, and they rack up several casualties along the path.
Jay moves through the woods toward the ship, confronting multiple aliens along the way. He defeats them with the sound weapon but is wounded by an alien zombie, portrayed by Dick Cherney. Despite the injury, he reaches the alien vessel and fires again, causing the ship to explode. With the jamming silenced, Penner can finally inform the government of how to halt the invasion, while Phyllis tends to Jay’s wound.
In the aftermath, the United Nations in New York receives thanks as Penner, Lamont, Phyllis Penner, and Major Jay are celebrated for saving the world from a covert, terrifying threat. The tale closes with a reminder of human resilience in the face of an unseen enemy and the power of sound to push back against the unknown.
