Traveling to Mars is Douglas Quail's singular obsession, a dream which he has had since childhood — one which his wife scorns and is rendered impossible by the fact that he, an ordinary office clerk on Earth, does not have the government clearance to go.
One day, Quail decides that he settle for an "extra factual" memory implant. This is a service offered by underground memory manipulators, who plant fake memories in clients for an exorbitant price. Quail asks for a memory of him traveling to Mars for one month implanted in him.
While the psychiatrists are sedating Quail, they discover that their patient actually has long suppressed memories of being a dangerous undercover assassin in Mars. They have just been erased by government agents, and they are coming to surface only now that his memory is being manipulated again.
The government agents who had erased his memory in the first place and have been keeping track of Quail the entire time are alarmed that their subject has regained his memory and try to detain him. Quail escapes their arrest however, and negotiates a compromise where they try to implant an even stronger memory in him to replace the one of being an undercover agent on Mars.
The psychiatrists identify Quail's strongest childhood fantasy, which is to be someone saving Earth from an alien invasion. However, during the process of the memory implant, they discover that this fantasy, too, is real. In a bizarre revelation of history, Quail had actually saved humanity from extinction by an alien invasion. The ending of the short story then leaves the reader on a comic note: which of Quail's narcissistic dreams have not turned out to be real?