The story takes place in the future. A professor invents a way to extraordinarily rapidly reproduce eggs using red solar rays… A Soviet worker, Semyon Borisovich Rokh, steals the professor’s secret and orders crates of chicken eggs from abroad. And it so happened that at the border the eggs of these creatures were mixed up with the chickens—and Rokh ended up with eggs of legless reptiles. He bred them in his own Smolensk province (that is where all the action takes place), and immense swarms of reptiles marched on Moscow, laid siege to it, and devoured it. The final picture is a dead Moscow and a huge serpent coiling around the bell tower of Ivan the Great.
Realizing the original pessimistic ending was unacceptable due to profanity, Bulgakov rewrote the ending of “Rokhovye eggs.” And as a result, a frost came and the reptiles died out..
For the writer’s luck, the censors saw the reptiles’ march on Moscow in “Rokhovye eggs” only as a parody of the intervention by 14 states against Soviet Russia during the Civil War (the reptiles were foreign, since they hatched from foreign eggs). Therefore, the capture of the scaly hordes of the capital of the world proletariat was perceived by censors only as a dangerous hint of a possible defeat of the USSR in a future war with the imperialists and the destruction of Moscow in that war.