At his boardinghouse in Rio de Janeiro, the Englishman James Marian is seen as handsome but eccentric. Then another boarder learns Marian's secret: a fusion of a female head and a male body, Marian is the creation of a surgeon with occult powers. Despite his wealth and mysterious abilities, Marian is unable to live fully as either a man or a woman, traveling the world in order to repress his sexual desire and withdraw from society.

Sphinx explores the binaries of science and magic, body and spirit, male and female, attraction and horror, presenting its sexually ambiguous protagonist with sympathy. Ornately descriptive, this 1908 neo-gothic novel exemplifies the era's taste for the sensual and the fantastic. With echoes of Mary Shelley's Frankenstein, it stands as a classic of Brazilian science fiction.