As a lone man drives along an empty desert road one night, a bright sphere in the sky hovers overhead, causing his car engine to die. Dazed by the blinding light, the man proceeds to Lab Central, a government outpost in the desert. After slugging a guard, the man breaks into the office of Dr. Hubbel Eliot, the lab's head scientist, transmits a ray aimed at the doctor's head, and then collapses, dead. Meanwhile, in another part of the lab, scientist Les Gascal mentions to his colleague, Arnie Culver, that the asteroid he has been tracking has unexpectedly changed course. As Arnie confers with Suzie, his computer, Eliot enters the room, causing Suzie to shut down suddenly. When Les informs him about the asteroid's new trajectory, Eliot discounts the information, puzzling Les. After Eliot leaves the room, Suzie recovers and confirms that the asteroid's destination is Earth. Les asks the military to destroy the asteroid before impact, and as missiles are trained on it, Eliot trembles in anticipation. When the missiles hit their target, Eliot collapses and is hospitalized. Surviving the onslaught, the asteroid plunges into the ocean off the Mexican coast. Believing that the asteroid may harbor some form of intelligence, Les and Arnie fly to Mexico to investigate, and are followed there by Vera Hunter, Les's sweetheart and assistant. As Vera and Les frolic in the surf, Eliot, confined to his Phoenix hospital bed, has a vision of the asteroid burbling under the sea. In Mexico that night, the earth begins to tremble, and the next morning, a massive metallic monster stands on the beach. Back at the hospital, Eliot's psychiatrist, Dr. Stern, reviews his patient's ravings about the "evil incubus that lives within him--a demon who dominates the inhabitants of an undiscovered world subsisting on atomic energy," a world, with depleted resources, that is scourging the universe for fresh supplies. In Mexico, meanwhile, Les, Arnie and Vera land a helicopter on the platform encircling the creature. When a hatch opens, they scurry back to the helicopter, and Arnie dubs the creature Kronos, after the evil monster from Greek mythology. In Phoenix, Eliot overhears Stern listening to a tape recording of his ravings and, after electrocuting the psychiatrist, confiscates the tape. With the death of his psychiatrist, Eliot is discharged from the hospital and returns to the lab to scrutinize a catalog of atomic resources within the Americas. Eliot telepathically directs Kronos to a power plant in Mexico, where the monster begins to march across the beach. After the monster drains the plant's power, Mexican fighter planes attack, but Kronos deflects their bullets and then blasts them from the sky. Kronos then continues its rampage through the desert, pillaging all hydroelectric towers in its path. Upon returning to Lab Central from Mexico, Les questions Eliot's decision to drop an atomic bomb on Kronos, fearing that it will enhance the monster's power. After discovering that Vera has learned of the events that transpired at the Phoenix hospital, Eliot attacks her in the lab's power room. Rushing to her aid, Les pushes Eliot into a high-voltage board, shocking him into a brief period of clarity in which he asserts that the only way to stop Kronos is to transform energy into matter. Now realizing that the atomic bomb will only fuel the monster, Les notifies the Pentagon to recall its bomber. He is too late, however, and Kronos hungrily absorbs the bomber into its force field. After the resulting atomic blast, Eliot collapses and an electronic field flows out of his body. With his last words, he reiterates that energy must be transformed into matter to rid the world of Kronos. Deciding that the monster must be destroyed with its own energy, Les devises an internal chain reaction. As Kronos lumbers toward the atomic bomb stockpile near Los Angeles, panic ensues. Just as Kronos reaches the outer limits of the city, a lone pilot wings his way toward the monster and drops a bomb that pummels Kronos with raw power, thus causing it to eat itself alive.