When United States Air Force intelligence receives word that an unidentified flying object it has been tracking has landed in a mountainous region in the western part of the country, intelligence head Gen. Knowland recommends consulting with scientists from nearby Pacific Technical University, but Col. Mathews advises maintaining secrecy in investigating the object. Knowland nevertheless contacts Dr. Karl Sorenson, an astrophysics expert and major advisor on the project that developed the atomic bomb. Karl joins a wary Mathews at the landing site where they discover a spherical object that Mathews suspects may be a weapon. Despite Karl’s observation that the hovering sphere appears innocuous, Mathews orders a guard placed around it. As the colonel and Karl leave, lodge owner and widow Kathy Grant and her young, paraplegic son Ken drive up full of questions about the object. Although displeased that the object’s landing has already been noticed by the local townspeople, Mathews arranges with Kathy to use the nearby lodge as a temporary Air Force headquarters. Irritated by Karl’s refusal to consider the sphere dangerous, Mathews asks Knowland to replace the scientist, but Knowland refuses. Back at the university laboratory, Karl excitedly tells his assistant, Dr. Richie, about the sphere and both men lament that current political conditions have placed barriers on consulting with certain international colleagues. At the landing site, Sgt. Gray orders the guards not to allow anyone near the object, but as Gray departs in a jeep, no one notices a strange glow emanating from the sphere that seems to be following Gray. Moments later, when Gray pulls into the lodge, he hears footsteps nearby, but sees no one. Inside, meanwhile, Mathews talks with Kathy, who regrets that for all the recent advances made by science, there is no cure for Ken, who has been diagnosed as having little more than a year to live. When Mathews leaves to make a phone call, Kathy is startled by a shadow-like figure walking through the room. Later that evening, sightings of the shadowy figure cause panic all over the community. The figure goes unnoticed, however, as it explores Karl’s lab and modifies a blueprint diagram. The next morning, Richie excitedly shows Karl the mysterious additions completing his photon chamber diagram. Convinced that the mysterious sightings and the diagram completion are proof of an alien from the sphere, Karl concludes the interstellar visitor must be benevolent. Diagnosing the traces of the visitor’s presence in the lab, Karl finds that the alien is made up of anti-matter, and dubs it “Cosmic Man.” Later, Mathews contacts Karl to inquire on his progress studying the sphere, but when Karl advises patience, Mathews declares that he is ordering the object moved to the base to be dissected. After Karl departs to join Mathews at the sphere, a strange pale-faced man with unusual glasses arrives at the lodge and asks Kathy for a room. Out on the hill, Mathews is frustrated by the inability of his men to move or penetrate the sphere. Karl and Richie conduct a number of tests on the object and discover the sphere’s capacity to turn light into energy and energy into potentially lethal sound blasts. Alarmed, Mathews pronounces the object a weapon and is adamant that it must be dismantled immediately. After Knowland arrives at the lodge, he and Mathews meet with Karl, who states that the object may have picked its landing location intentionally as it is near both ion propulsion and radiation plants. Disturbed, Knowland agrees with Mathews’ decision to dissect the sphere. Mathews then states that he has contacted another scientist who is on his way from Washington, D. C. to provide another opinion. A little later, the lights in the lodge suddenly go out and the shadow figure emerges, identifying itself as the alien visitor. Dismissive of Knowland’s questions, the alien explains his people’s interest in sharing knowledge throughout the galaxy and praises scientists as the hope of an immature mankind. The alien reveals that Earth has long been studied and will continue to be investigated, but the atmosphere is a strain on his kind, limiting their visitations. The alien asks to be allowed to depart the following day without interference, but Mathews interprets the request as a threat and shoots the figure. The alien is unaffected by the attack and disappears. Knowland then orders the alien’s capture and destruction. Karl argues with Mathews regarding the alien, but the colonel reveals that he has learned that ingredients for constructing an atomic weapon stored in nearby plants have all been contaminated, suggesting the alien’s involvement. When Karl insists the contamination indicates the alien means well and that it must be saved, Mathews orders the scientist placed under guard. The night, while Mathews’ men set up a magnetic field around the sphere to prevent the alien from entering it, Kathy discovers the stranger in Ken’s room, playing chess. The next morning, Kathy is horrified to discover Ken missing and tells Karl, who immediately suspects the stranger and the alien are one and the same. Kathy accompanies Karl to the sphere, where the scientist reports Ken’s disappearance to Knowland. As the newly arrived scientist from Washington, D. C. oversees the continued application of the magnetic field, the group is startled when the alien abruptly materializes in front of them carrying Ken. The alien requests the magnetic field be turned off so that he might enter his ship, then lays the boy on the ground. The field is shut off but as the alien walks to the sphere, the new scientist insists the being must be studied and turns on the magnetic field, causing the alien to collapse. Outraged, Karl shuts off the magnetic power as Kathy runs to Ken. To Kathy’s amazement, Ken stands and walks toward her. As Kathy hugs her son, a light beams from the sphere onto the alien and both disappear. Karl embraces Kathy and declares his certainty that Cosmic Man will one day return.