When a startling number of Americans prominent in the fields of science, math or technology mysteriously vanish, two NSA field agents, Ruthanne Carter and Larry Tracker, investigate the disappearances. Unknown to them, Caden Jordan, a highly competent detective, generates strong doubts that certain missing persons vanished of their own accord. The two agents and the detective compile an array of intriguing information that leads them, in company with other specialists within the NSA, to conclude that an alien "Entity," for some enigmatic reason of his own, is surreptitiously abducting persons with certain abilities and transporting them to an alternate Earth in a parallel universe. When Ruthanne Carter vanishes, Larry realizes that she has been abducted by the Entity. Desperate, owing to his love for Ruthanne, he voluntarily puts himself in a position that increases his chance of being abducted himself. He becomes the next person to vanish.

Ryan Bigelow, a geneticist who was the first person to disappear, awakens within a mysterious, shimmering dome. He emerges to find himself in a wild, unpopulated land that he suspects to be the American West, even though it contains an old, abandoned stone city that does not resemble any ancient site in America. Bigelow, who finds artifacts in the city that enable him to survive, exercises a remarkable talent for leadership as new arrivals emerge daily from the dome. When Ruthanne Carter appears, she finds that Dr. Saul Steiglitz, a renowned physicist, agrees with the NSA's conclusion that an alien "Entity" has teleported the MPs to a parallel universe. Dr. Arthur McConnell, a youthful mathematical genius, concurs in that belief. The final abductee to emerge from the dome is Larry Tracker.

When the Entity contacts the group, he succeeds in speaking through Ruthanne Carter, who alone of all those snatched has a mind that can withstand the trauma caused by the Entity's invasion. The horrified listeners learn just what the Entity is and discover what he wants. Assuming right from the start that the Entity can't be trusted, they assert themselves, despite knowing that the ruthless alien can kill them instantly. Refusing to let themselves be intimidated, they find weaknesses they can exploit in his mental makeup. The tension escalates as the abductees negotiate with the Entity, struggle against him, and finally devise a means by which they hope they can outwit the murderous alien.