In some respects the title character, Ernest-Jean Sarrasine, is the protagonist, but his story is framed as a tale that the unnamed narrator tells to Madame Beatrix de Rochefide. She is a greatly admired beauty, and the narrator is intent on seducing her. The narrator, although he frequents the Paris salons, is interested in truth as well as beauty. The story he tells is concerned with the model for a painting of Adonis on view at the party they are attending.

The ideal woman, whom Sarrasine loves, is an opera star with the stage name La Zambinella. Sarrasine is misled, however, as she is actually a castrato. Sarrasine is described as passionate and artistic, and sees the singer in Rome where he is pursuing sculpture. He runs afoul of the singer’s patron, a powerful cardinal. The plot strands are tied up when it is revealed that La Zambinella is not only the painting’s model and a guest at the party but also the Countess de Lanty’s uncle.

The action takes place at a ball in the home of the Count de Lanty, who is wealthy man but physically unattractive and dull in temperament. Other characters are his wife and two children, all very good looking. The teenage daughter, Marianina, is an ideal of purity and beauty with a lovely voice. The son, Filippo, is much in demand as a potential husband.