This compact tragedy is told by a narrator who, at a dinner, hears H--- relate the life and death of an eccentric American painter, “Mr. Theobald,” during his youth in Florence. Theobald first appears one moonlit midnight in the Piazza della Signoria—ardent, strangely dressed, and full of rhapsodies about David, Cellini’s Perseus, and the vanished “days of illumination.” He declares himself a convert to the pure masters, professes never to have sold a picture, and vows to create a single supreme work: a Madonna that will condense the perfection of the Italian tradition.

Over a fortnight the narrator becomes Theobald’s companion and guide through the city’s churches and galleries. Theobald is a study in devoted idealism: learned, sentimental, poor, habitually preparatory. He talks of art as worship, of idealism as the only true method, and treats observation and private devotion as equivalent to production. He has long cherished a modelless vision of the perfect Madonna, but claims to have found in a humble woman of the Mercato Vecchio—Serafina, a plain, pious, middle-aged needlewoman—the living type for his work. He rescues and sustains her; she yields him a grateful, ambivalent patronage. Meanwhile Mrs. Coventry and others, after initial enthusiasm, grow sceptical; gossip paints Theobald as an amiable impostor who talks more than paints.

The central irony is Theobald’s paralysis of execution. He accumulates impressions and notes, adores a model in private, but procrastinates—waiting for a fitter moment of inspiration—and thus loses the freshness he once observed. When the narrator, with blunt tact, tells Theobald that Serafina has visibly aged, the spell breaks. Theobald, struck by the sense of wasted years, collapses into despair and a feverish decline. The narrator discovers the celebrated “Madonna” only as a blank, discoloured canvas in the starving artist’s squalid room. Theobald dies; his funeral is poorly attended. The narrator inherits the titular masterpiece—meaning, in bitter truth, the empty promise—and chooses never to exhibit it.

The story pits idealism against action: reverent preparation degenerates into dawdling; worship of beauty without workmanship becomes self-delusion. Florence—its museums, saints, and patrons—forms both a crucible of aspiration and a stage for comic, sometimes cruel, human commerce (embodied by a rival sculptor of satirical “cats and monkeys”). The tale is elegiac and ironical: it mourns a sensitive, sincere temperament destroyed by its own fastidiousness, and observes, with a cool, bitter eye, how the marketable, caricatured arts prosper where patient genius perished.