As Dr. Russell Martin, a space exploration scientist working for the Defense Department, and his bride Carol drive down a deserted desert road, a flying saucer spins in front of their car’s windshield. Upon reaching his lab, Russ replays the tape recording he was dictating when the craft appeared and detects the sound of the saucer. Soon after, General Hanley, Carol’s father, arrives at the base to inform Russ that the artificial satellites that he has been launching into space have all come crashing back to Earth. On the eve of another launch, Carol and Russ lock themselves in Russ’s underground lab to observe the event. Above ground, meanwhile, a flying saucer lands on the base and disgorges a group of spacesuit-clad aliens, who proceed to destroy the entire area. Watching the carnage from their monitor, Carol and Russ witness the aliens force General Hanley into their spaceship. Afterward, Russ tries to document the events on his tape recorder, and when the machine slows down, he deciphers a message from the aliens recorded the previous day announcing their impending arrival. After Russ and Carol are rescued and taken to the Pentagon, Russ plays the recording for government officials, who remain skeptical about Russ’s story of sighting a flying saucer. When Russ asks to meet with the aliens, he is told that he must wait for Cabinet approval. Sequestered in his hotel room, Russ makes contact with the UFO on his short-wave radio and schedules a meeting. When Russ leaves the hotel over Carol’s objections, Carol notifies Russ’s escort, Major Huglin, and they set out after him. As Russ reaches the designated meeting place, Carol and Huglin arrive and the saucer then appears and invites them all inside. After taking off, a disembodied voice explains that the aliens shot down the satellites because they thought they were weapons. The voice continues that they and their fleet of saucers circling the globe are survivors of a dying solar system. The voice then menacingly demands to confer with world leaders. Just then, General Hanley, in a zombie-like state, stumbles into the chamber, and the voice informs them that the aliens have sucked out his mind and filed it in their memory bank. After Russ agrees to deliver their message, the craft lands. Upon returning to the Pentagon, Russ suggests developing a new kind of weapon to use against the aliens before they can destroy the Earth. As Russ grapples with the concept of using a high-wave frequency to disrupt the UFO’s magnetic field, a spy device from the saucer hovers over the laboratory and is shot down by Major Huglin. With a sense of urgency, Russ speeds to Washington before the aliens can decipher his plans, and the saucer pursues him. When it lands, an alien steps out and is gunned down by Huglin. Upon removing the alien’s spacesuit, Huglin finds an ancient humanoid. Taking off once again, the saucer demolishes a bomber plane and then expels the body of Carol’s father. At the Pentagon, meanwhile, scientists analyze the spacesuit and decode the aliens' plan of attack. Soon after, an alien voice addresses the people of the Earth, announcing that in nine days a violent explosion on the sun will occur, followed by the invasion of the aliens. With time growing short, Russ goes to Aberdeen to perfect the interference units and orders are given to evacuate Washington. The sun’s eruption spawns a series of fierce storms that disrupt all transportation and communication systems, thus preventing a mass evacuation. As the saucers occupy the skies above the city, Russ and a convoy of trucks bearing the interference weapons arrive. After Russ shoots one of the saucers down, Carol runs to him. The saucers reign destruction on Washington, but Russ and his convoy pursue them through the streets, shooting them down one by one. After blasting the Supreme Court building, the last saucer hovers above the Capitol building. Aiming his weapon at the saucer, Russ sends it crashing down into the Capitol, bringing the invasion to an end. The space exploration program then continues under Russ’s guidance, and with peace restored, Russ and Carol take a much needed vacation.