The summary of The Slum by chapter, in nine blocks that cover the 23 numbered chapters, follows; the novel has no chapter titles.
Chapters I and II: João Romão inherits his employer's shop and starts living in privation. He keeps the savings of Bertoleza, an enslaved woman, and reads her a letter of freedom that he himself forged. With stolen stone, he builds the São Romão Tenement next to the townhouse of Miranda, who envies him and dreams of a title.
Chapters III to V: the tenement wakes on a working morning, and the book shows the residents tub by tub, among them Pombinha. João Romão hires the quarryman Jerônimo for seventy milreis, and he arrives with his wife, Piedade, at room 35.
Chapters VI and VII: on a Sunday, Rita Baiana returns to the tenement. Miranda shouts from the window against the noise, and at night the chorado of Firmo and Porfiro silences the fado and ties Jerônimo to Rita's dance.
Chapters VIII and IX: Jerônimo falls ill, and Rita nurses him. Little by little he trades his villager's habits for those of the land, and Piedade seeks out the Witch. Leocádia is evicted, Florinda becomes pregnant, and João Romão refuses to pay her dowry.
Chapters X and XI: Miranda becomes Baron of Freixal, and João Romão feels what he lacks. On a night of samba, Firmo wounds Jerônimo with a razor, and the tenement unites against the police. Pombinha spends an afternoon at Léonie's house.
Chapters XII to XIV: Pombinha marries. The rival tenement, the Cabeça-de-Gato, is born, and João Romão changes his clothes and his ambitions and arranges with Botelho the path to Zulmira, Miranda's daughter. Jerônimo returns from the hospital determined to take revenge.
Chapters XV to XVII: Jerônimo, with two companions, lures Firmo to the Praia da Saudade and kills him, and goes to live with Rita. Piedade fights with Rita, the capoeiras of the Cabeça-de-Gato invade the São Romão to avenge Firmo, and the battle ends only when the Witch sets fire to the tenement.
Chapters XVIII to XX: in the fire, João Romão takes Libório's bottles of money, and the insurance pays for the rebuilding. He builds a townhouse taller than Miranda's and courts Zulmira, the tenement becomes São Romão Avenue, and Piedade takes to drink.
Chapters XXI to XXIII: with the marriage to Zulmira settled, João Romão resolves to return Bertoleza to her former master. The tenement becomes aristocratic, and Pombinha becomes a cocotte. The former master's son arrives with two policemen, Bertoleza kills herself, and a commission of abolitionists brings João Romão the diploma of benefactor member.