In the distant future, an uninhabited Earth is discovered by the Ganae, an advanced, expansionist, non-anthropoid species surveying potential colonies. Earth has suffered a mysterious catastrophe; all animal life is gone, but there is no sign of warfare or of any other obvious cause, and the overgrown ruins of largely-intact cities are littered with the skeletons of humans who seem to have died without violence.

Only a minuscule fraction of stars possess planets, making them extraordinarily valuable; the Ganae have by happenstance discovered a technology they call the "locator," which can determine which ones do. They also have "reconstructor" technology, capable of restoring an intelligent being (with all of its memories) to life as long as a minimal biological sample remains. Curious as to the reason for the depopulation of Earth, the survey crew locates a museum and begin reviving humans in order to interrogate them. Their initial efforts meet with limited success: the first subject is an Egyptian pharaoh who interprets the Ganae as gods or demons, while the second is a Prohibition-era American who thinks he is having a drunken hallucination. The third, however, is an advanced human from approximately 4000 AD, who recognizes the Ganae as aliens but can tell them nothing about the catastrophe. The earlier resurrectees had been summarily executed once the Ganae had been done with them; however, this proves difficult with the third, who manages to take telepathic control of some of the advanced atomic technology on display in the museum and uses it to defend himself, killing several guards in the process. The Ganae are forced to flee back to their mothership, from where they destroy the museum and surrounding city with an atomic weapon.

The survey team rules Earth suitable for colonization, but is concerned that the unknown cause of humanity's extinction could conceivably threaten a future Ganae colony. The captain reluctantly decides to revive another human for questioning. Immediately after awakening, the fourth human teleports away; he reappears before the survey team a few moments later, and effortlessly shrugs off all attempts to harm him, in the process demonstrating "mental control of nucleonic, nuclear, and gravitonic energies." The anxious Ganae - who have long feared encountering a species superior to themselves, and being held to account for the genocides they have committed - immediately destroy the locator and reconstructor aboard their mothership. Slightly reassured, they attempt to negotiate with the fourth human, who freely reveals the cause of Earth's depopulation: a "nucleonic storm" dozens of light-years across, extending beyond humanity's limited range of teleportation. Not having the Ganae locator, humanity had only managed to find one other habitable planet, which was also in the path of the storm. When the Ganae assert that they must colonize Earth due to the great population pressure within their empire, the human suggests that they instead limit their population. This infuriates the Ganae, for whom expansion is a biological imperative at the center of their society; the human calmly informs them that if they will not control their population, "we will." The Ganae leave, promising to return with a fleet large enough to overwhelm the human's powers and reduce the surface of the Earth to slag.

En route to the nearest Ganae outpost, the aliens are shocked to discover the human aboard their mothership. They realize that range of his teleportation is much greater than he has led them to believe, and deduce that he intends to accompany them back to their world, steal the reconstructor technology, then teleport back to Earth and revive more of his kind before the Ganae can return; even an entire fleet could do nothing against multiple humans with the same powers. Unwilling to transmit a warning home for fear that the human might trace their transmission beam and teleport ahead to its destination, the Ganae decide to steer their nearly-indestructible mothership into a blue-white star and destroy the guidance system. Moments before the ship is destroyed, one of the Ganae comes to the horrifying realization that the human's brief disappearance upon his awakening had given him enough time to teleport aboard the ship and learn the secrets of both the reconstructor and the locator; he had only returned aboard to manipulate the Ganae into committing suicide before they could warn their empire, ensuring that "no alien mind" will have forewarning of the impending rebirth of the human race.

• Full text of "The Monster"