One, No One, and One Hundred Thousand tells how an offhand remark by his wife about the nose of her husband, Vitangelo Moscarda, makes him discover that he is not one, neither for himself nor for others, and how, to recover the unity he has lost, he dismantles his own life and ends up in an almshouse for beggars, nameless.
In the first three Books, Moscarda, twenty-eight years old, rich and idle, heir to a bank in the city of Richieri, hears from Dida that his nose leans to the right. The remark takes him to the mirror, to the idea that each person sees him in a different way, and to the conclusion that he is one hundred thousand Moscardas. He speaks the whole time to a reader, discovers that Dida loves a husband named Gengè whom she herself built, and sees his father, a banker to him, as a usurer in the eyes of the city.
In Books IV and V, he puts the thesis to the test. He has Marco di Dio, the man who hates him most, evicted, and soon gives him a house; the crowd that called him a usurer starts shouting "madman." When Dida's laughter wounds him at a point no image can reach, he orders the bank closed and pushes his wife into the armchair.
In Books VI to VIII, Dida leaves, he seeks out the bishop, takes a shot from Anna Rosa and, on the plan of Canon Sclepis, surrenders everything to found an almshouse for beggars. The novel ends with him at the asylum, nameless and without a mirror, among trees, clouds and bells heard from outside.