This suspenseful science-fiction thriller delves into the terrible sequence of events that unfold in the life of two astronauts, who return to Earth after a failed mission. While on a space-walking mission, Spencer Armacost, a NASA astronaut, and fellow astronaut Alex Streck, experience an explosion from a satellite which results in a communication loss for two minutes between the astronauts and Earth.
After returning to their respective spouses, the two astronauts never speak about their ordeal. Streck grows increasingly agitated and bleeds to death during a party. His death is ruled as a stroke by NASA. While still in mourning for her lost husband, Streck's wife experiences delusions and tells Spencer's wife Jillian that her husband had been listening to an unknown entity on the radio who is now inside her. She then commits suicide by holding a radio while sitting in a running shower.
Spencer retires from NASA and takes an executive position in New York City for a company called McClaren. Jillian questions him about what happened during the time they lost contact. He answers with a vivid description but displays a suspicious change in personality and becomes very aggressive during their subsequent sex. Jillian soon becomes pregnant with twins.
During dinner, Spencer and a co-worker describe a new aircraft their company is developing that can turn off all other machines, rendering modern warfare obsolete. A former NASA employee, Sherman Reese, tells Jillian that Spencer's medical data (including his signature) has changed since the accident, that Streck's wife had been pregnant, and that Spencer is no longer himself. Jillian does not believe Reese, noting that he had been fired for what appeared to be psychotic behavior, but she finds she cannot let go of Reese's statements.
Jillian calls Reese and learns that Streck's wife had also been pregnant with twins. Jillian makes arrangements to meet Reese to learn more, but Spencer runs into him and leads him away. Jillian is unable to get in touch with Reese again but discovers that he left a note leading her to a VHS video tape. The tape shows evidence of an alien audio signal that, he postulates, was used by aliens to beam themselves into the bodies of the unsuspecting Spencer and Streck, and her twins are likely intended to be "Twin-Computers" meant to fly McClaren's new aircraft.
Jillian dreams that Spencer had been possessed by an extraterrestrial and acquires medication that will cause her twins to be aborted. The twins, however, will not let her take the pills and summon Spencer. He assaults her to protect the twins, and causes her to fall down the stairs. Jillian awakens in the hospital and is greeted by Spencer, who tells her that nothing is going to happen to the twins.
In a dream, Jillian sees her sister killed by Spencer because she caught Spencer with Reese's briefcase. Jillian leaves the hospital and fails to evade Spencer since he can communicate with the twins. Back at home, Jillian finds her dead sister and floods the floor with water while holding a radio as Streck's wife had done. Spencer arrives and admits that "he" (the alien) killed Spencer. Using telekinesis, he moves Jillian, who is sitting on a stool, out of the water, but Jillian electrocutes him as she raises her feet out of the water. Spencer's true alien form, a tentacled energy being, leaves Spencer's body and transmits itself into Jillian, stopping the electrocution.
Years later, Jillian has re-married and sends her twin sons off on their first day of school. Before they get on the bus, they offer a stern look at their mother, while she embraces their new stepfather, a "non alien". They then smile as Jillian assures the new stepfather that he is their father now.