Lee Wilder’s production company, Planet Filmplays, usually producing on a financing-for-distribution basis for United Artists, made this film for RKO Radio Pictures distribution.
Dr. Douglas Martin (Peter Graves) is a nuclear scientist working on atomic bomb tests. While collecting aerial data on a United States Air Force (USAF) atomic blast at Soledad Flats, he loses control of his aircraft and crashes. He appears to have survived, unhurt, walking back to the air base with no memory of what happened. On his chest is a strange scar that was not there before the crash.
At the base hospital, Martin acts so strangely that the USAF brings in the FBI to investigate, thinking he might be an impostor. He is eventually cleared but told to take some time off. Martin protests being excluded from his project while on leave.
When an atomic test is set off without his knowledge, Martin steals the data, then goes back to Soledad Flats and places the information under a stone. An FBI agent follows him, but Martin is able to elude him until he crashes his car. Now back at the hospital, he is given truth serum. Deep under the drug’s influence, Martin tells a story about being held captive by space aliens, led by Denab, in their underground base. The aliens, with large, bulging eyes, are from the planet Astron Delta, ruled by a being called The Tala. They had revived his lifeless body as he had died in his aircraft.
The aliens plan to exterminate humanity using giant insects and reptiles, grown with the radiation absorbed from our own atomic bomb tests. Martin intuits that the aliens use stolen electric grid power to control their powerful equipment. This so that the A-bomb’s released energy levels can be predicted and then balanced. The aliens wiped his memory and hypnotized him into collecting the data for them.
The FBI agent (Steve Pendleton) and the base commander (James Seay) are skeptical of this incredible story and keep him confined at the hospital. Nevertheless, the attending physician says that Martin genuinely believes that what he told them is true.
With calculations made with a slide rule, Martin determines that if he shuts off the power to Soledad Flats for just 10 seconds, it will create an overload in the aliens’ equipment. So he escapes from the hospital and goes to the nearby electrical power plant, where he forces a technician to turn off the power. After 10 seconds, the alien base is destroyed in a massive explosion, saving the Earth from conquest.