"The Underdweller" is a variant title. It has also appeared under the title "Small World" and "The Small World Of Lewis Stillman."
Lewis Stillman loots the convenience stores of Los Angeles at night, creeping past and hiding from small gangs of inhuman enemies: “They came closer, crowding the walk, their small dark bodies crowding the walk, six of them, chattering, leaping, cruel mouths open, eyes glittering under the moon.” Stillman ruminates on lost love and the precariousness of his existence. He is lonely and searches for survivors of his like kind. Three years of searching Los Angeles has convinced him that he is the last man alive in the city. Stillman sleeps in the storm drains, tormented by dreams of women or of being caught. The storm drains are how he survived the unprovoked attack by aliens that killed every other man and woman six years earlier. For three years he worked with his enemies and for three years he has run from them. Stillman fashions human figures for company and argues with them as he goes insane. Venturing forth to find books to read, he comes upon a bookstore they have destroyed, ripping the pages out of thousands of volumes. Stillman has been lured into a trap and they attack him in force. He kills as many as he can with a machine gun, but is overwhelmed in a tide of feral children.