Two thousand years in the future, the human race is on the verge of extinction: the atmosphere has filled with agnoton gas, an inert substance to which all humans are allergic, and an alien invasion is doing away with those who have not yet succumbed to the gas. Three people only remain safe from this threat in a self-sustaining retreat with filtered air: the scientist Kirth-Labbery, his daughter Lavra, and the paleolinguist Vyrko.
Kirth-Labbery dies of a heart attack, and it seems there can be no hope left. Vyrko passes the time reading old pulps that had been found in a time capsule and ensuring the continuation of the human race with Lavra. He has found a most curious coincidence: while many of the science fiction stories have contained elements that turned out to be true, all the stories written by Norbert Holt predict the future absolutely correctly, down to the last detail. At last, he finds a final unfinished story by Holt--published posthumously--which details the very situation Vyrko is now in--even mentioning him, Lavra, and Kirth-Labbery by name.
At the direction of the story, Vyrko activates a device left behind by Kirth-Labbery, which promptly transports him to the distant past: 1948, two thousand years ago. Having no other saleable skills, Vyrko tries his hand at writing, but his futuristic style is unsuited to the tastes of the twentieth century. Finally, he decides to write in a genre where his style will not be a hindrance: science fiction. Having prepared his first story, he realizes the truth, and signs it Norbert Holt.
This time around, though, his editor decides to burn the unfinished story, and the next morning, she cannot remember ever meeting a man named Norbert Holt.
This story features an extremely circumspect way of saying "Vyrko impregnated Lavra":
Lavra, incidentally, is protrayed as a weepy, uncurious, passive person whose sole saving grace is her beauty. It's rather grating.