Pedro Rubião de Alvarenga, whom everyone calls Rubião, is the protagonist: a schoolteacher from Barbacena who inherits the fortune of the philosopher Quincas Borba, goes to live in Rio, and ends up mad, believing himself to be Napoleon III.
In Barbacena, he runs a boys' school, which he closes to care for the ailing philosopher, of whom he becomes the only friend. He looks after him nearby for six months and listens, without understanding, to the doctrine of Humanitas. When a letter arrives in which his friend says he is Saint Augustine, he takes him for mad, hides the letter from the doctor for fear that the will will be annulled, and calculates the legacy. His remorse, the narrator says, is "easy, short-lived."
The will makes him universal heir. In Rio, Rubião moves to a house in Botafogo, receives dinner guests at his table, desires Sofia, the wife of his guide Palha, enters the Atalaia, the newspaper of the politician Camacho, and becomes Palha's partner. Upon inheriting, he understands for the first time the allegory of the starving tribes and sees himself as a victor: he even composes in his head a seal bearing the motto "To the victor, the potatoes."
After the partnership is dissolved, he comes to believe himself the emperor Napoleon III, is committed, flees to Barbacena with the dog, and dies there, placing on his head a crown that only he sees.