Electrical engineer Dave Brewster and his family are forced to move from San Francisco to Southern California when Dave's company is hired by the U.S. government to work on a new intercontinental missile. While driving down the California coast, Bud and Ken, Dave's two pre-teen sons, hear an eerie sound. Though their parents are unaware of what is happening, the two boys witness an alien from outer space being teleported to Earth. Later, while playing on the beach, Bud and Ken meet the children of the other technicians working on the "Thunderer" missile project, who then show the two boys the missile's launch site. Meanwhile, Dave and the other engineers are briefed on the current state of the project by their supervisor, Col. Manley, who informs them that the goal of the Eagle Point Missile Project is to launch a hydrogen bomb into outer space, where it will orbit the Earth until its payload is deployed. Unknown to their parents, the technicians' children have come under the mind control of the alien, who communicates with them through Bud. When an intoxicated Joe Gamble tries to hit his stepson Tim with a tree branch, the alien intercedes and Joe is later found in his trailer, dead from shock. Back in his family's mobile home, Bud tells his parents about the alien. Dave is then taken to the rock-like alien, which he brings back to their trailer, despite the protests of his wife Ann. The next morning, the alien has doubled in size, and Bud tells his parents that they must keep it safe and warm until nightfall. When their parents continue to argue over the fate of the creature, Bud and Ken return the ever-growing alien to its cave. Soon thereafter, Dave is informed that the "Thunderer" is being launched that night. With final preparations for the launch being made, Dave attempts to tell Manley and Dr. Wahrman, the rocket's designer, about the alien, but he is stopped telepathically by Bud and collapses onto the floor. Taken to the infirmary, Dave is stopped from leaving by the sudden appearance in the doorway of his two sons. Later, Bud uses mind control to force a rocket fuel truck off the road. Meanwhile, two other children use similar means to shut down the missile center's phone system. Looking for his young daughter Eadie, Hank Johnson enters the alien's cave, and the sudden shock of encountering the creature causes him to be hospitalized. Back at the missile's control center, Wahrman ascertains that the children are the common link between the sudden rash of bizarre occurrences. Wahrman then goes to the infirmary and tells Dave that he suspects a non-human force is behind the incidents. Learning about the alien, Wahrman is taken to its cave by Dave, where the scientist confronts the extraterrestrial and begs it to release the children from its control. When the alien refuses to communicate with him, Wahrman rushes back to the control center and arrives just minutes before the blast-off. After the rocket fails to launch and the "Thunderer" is destroyed, Dave, Wahrman and Manley hurry to the alien's cave, but are stopped from entering it by the children. The alien then emerges from the cave and is beamed back into outer space. When Manley questions the creature's actions in destroying this one missile, Bud tells the major that children all over the world have been doing the same thing at the same time to their countrys' missiles, giving the Earth a second chance at a nuclear-free life.