After what appears to be a meteor crashes in a gulley in the San Gabriel Mountains east of Los Angeles, scientist and Pacific Technical professor Clayton Forrester drives to the site. The blackened, cylindrical object has attracted a crowd of onlookers, including Sylvia Van Buren, a library science teacher from the University of Southern California, who knows Clayton by reputation. Unable to use his Geiger counter on the fiery hot object, Clayton decides to spend the night in the area and return to the gulley the next day. Sylvia and her uncle, Pastor Matthew Collins, offer Clayton their home and invite him to a square dance that evening. While Clayton and Sylvia are enjoying the dance, three locals who have been assigned to watch the object are startled when a previously hidden lid unscrews and a long-necked, metallic probe with a pulsating red "eye" emerges from the object's top. Although terrified, the men attempt to greet the probe, carrying a white flag and declaring their friendship. The probe studies the men for a few seconds, then shoots out a death ray, obliterating them. At the same moment, the power goes out at the dance and all the guests's wristwatches stop. After Clayton determines that everything has become magnetized, the sheriff drives up to announce that a fire has broken out in the gulley. Clayton, the sheriff and his deputy rush to the site and are immediately targeted by the probe. Sensing danger, the deputy races off in the patrol car, while Clayton and the sheriff dive behind some rocks. The probe shoots some rays, annihilating the patrol car, but missing Clayton and the sheriff. After a second object streaks across the sky and lands nearby, soldiers and ordnance from El Toro Marine Base are called to the scene and arrive with a radio reporter and other scientists. When an Air Force plane flies over the gulley, the probe begins firing at it, convincing Clayton that the object is the product of extraterrestrial intelligence, probably Martian. Later, reinforcements from the 6th Army Command, led by Gen. Mann, roll in, and Mann reveals that space ships have landed all over the world and that once they become active, phone lines and other means of communication are rendered useless. Noting that the two southern California sites are the only ones that have been militarily surrounded, Mann tells Clayton that their operations will be a guide for the rest of the world. At dawn, as the Army prepares to attack, a disc-shaped craft, to which the probe is attached, rises out of the gulley on invisible magnetic legs and starts "walking" toward the soldiers. Disregarding protocol, the pacifistic Matthew steps out to meet the craft and two others that have emerged from the gulley and, while reciting the 23rd Psalm, is disintegrated by death rays. Army tanks and artillery then bombard the discs, but enshrouded in an electromagnetic force field, the discs prove impenetrable. After many soldiers are killed by the advancing crafts, Mann orders a retreat and heads for Los Angeles. Clayton, meanwhile, escapes with Sylvia in his airplane, but is soon forced to crash-land. Clayton and Sylvia flee and hide while the discs encircle the downed plane. Sylvia falls asleep in Clayton's arms, and later, after they have found refuge in an abandoned farm house, Clayton reassures Sylvia that they will find a way to destroy the Martians. Suddenly, another space vessel crashes into the side of the house and Clayton is knocked out. When he revives hours later, a terrified Sylvia informs him that more ships have landed in the hills, and they are blocked in. Another probe, this one with a red, green and blue "eye," thrusts itself into the house, and Clayton hacks it in two with an ax. After Sylvia catches a glimpse of a small, long-armed creature outside, the creature sneaks up behind her and touches her with its spindly, three-fingered hand. Clayton hurls the ax at the creature, and the creature, whose wide, flat head boasts a single, three-colored eye identical to the probe, scurries off, screeching in pain. In the confusion, Clayton and Sylvia slip away, and later, while world leaders meet to discuss the plight of the planet, stagger into Pacific Tech with the hacked-off probe and a scarf stained with alien blood. An examination of the blood reveals that the Martians are anemic, and the probe, which the scientists speculate mimics the aliens' actual eyes, is dissected to demonstrate how their vision works. Government and military leaders in Washington, D.C., meanwhile, decide to drop an atomic bomb on the California invaders, but the aliens' force fields again prove impervious. Calculating that they have only six days to stop the aliens, the Pacific Tech scientists prepare to leave for Colorado, where they hope to devise an effective attack strategy. As Los Angelenos frantically evacuate, Clayton sends Sylvia off on a school bus with the other scientists, then follows in a truck. In the downtown area, however, the truck is beseiged and stolen by hysterical citizens, desperate to get out of the city. Clayton is abandoned on the street and, after finding a torn-off school bus sign, begins to search for Sylvia. Recalling a story she told him about her childhood, Clayton goes from church to church looking for her, while the alien ships begin their assault on the city. The churches are filled with frightened people, and when Clayton finally locates Sylvia, they embrace as a minister prays for a miracle. Just then, one of the ships crashes into a neighboring building, and silence fills the air. Outside, Clayton and the others see the craft door open and a Martian arm flop down. The alien then dies, and other ships begin to crash around it. The Martians, who have contracted bacterial infections from the Earth's atmosphere, expire, and to the world's relief, the invasion ends.