What happens is the opposite of what was expected, or of what someone planned, in a way that reveals something about the characters or about the world of the work.
In The Slum
Era uma comissão de abolicionistas que vinha, de casaca! trazer-lhe respeitosamente o diploma de sócio benemérito, a committee of abolitionists came, in formal dress, to respectfully bring him the diploma of honorary member.
The abolitionists come to honor as a benefactor the man who has just returned an enslaved woman to captivity: what happens is the opposite of what the honor implies, and the book closes on that clash.
Chapters XXI to XXIII: Bertoleza's End and Romão's Rise, the narrator