The narrator is Bento Santiago, the same Bentinho of the past, now old. He lives alone with a servant in a house in Engenho Novo, a remote neighborhood of Rio, which he had built as a copy of the Matacavalos house where he was raised. The neighbors call him Dom Casmurro, and it is with this nickname that he titles the book.
He says he wanted to "tie the two ends of life together," restoring adolescence in old age, and that he did not succeed. The book is born from the failure of the house: it was written to vary the monotony of his days.
Because Bentinho is both narrator and character, the reader knows only what he heard, saw and remembers, filtered through decades. He himself warns that he cuts scenes and that he prefers books that omit to those that are confused, in which "anything can be slipped in." For this reason each fact of the plot, especially the accusation against Capitu, reaches the reader as the version of only one party.