The sudden inheritance of a vast fortune by a naive schoolteacher triggers a descent into madness and social disillusionment. Rubião, a provincial teacher, inherits the wealth of the eccentric philosopher Quincas Borba under the condition that he cares for the man's dog, who shares the philosopher's name. As Rubião moves to Rio de Janeiro, he attempts to navigate the complex social hierarchies of the Brazilian Empire while grappling with the philosophical doctrine of Humanitism. The narrative, presented with a detached and ironic third-person perspective, tracks his psychological disintegration as he struggles to distinguish between genuine friendship and opportunistic exploitation.

Readers frequently highlight the author's biting wit and his ability to balance philosophical inquiry with character-driven narrative. Discussion often centers on the protagonist's tragic trajectory and the cynical portrayal of human nature inherent in the Humanitism philosophy. Critics emphasize the text's proto-modernist structure, noting how the author avoids sentimentalism in favor of a clinical, often cold, examination of social dynamics. The work is widely regarded as a cornerstone of Latin American literature, praised for its linguistic precision and its enduring relevance to the study of power and greed.