On a lovely day in May, 1868, Christopher Newman, a wealthy American businessman, sits down in the Louvre with an aesthetic headache, having seen too many paintings. A young Parisian copyist, Noémie Nioche, catches his eye, and he agrees to buy the painting she is working on for the extravagant price of 2, 000 francs. Shortly thereafter, Newman recognizes Tom Tristram, an old friend from the Civil War, wandering the gallery. Newman explains that he has made quite a fortune and now, having realized the inanity of seeking competitive revenge on his fellow businessmen, has decided to move to Europe to enjoy his wealth. Over dinner, Newman admits to the Tristrams that he has come to Europe to find a wife to complete his fortune. Mrs. Tristram suggests Claire de Cintré, the beautiful and widowed daughter of an impossibly aristocratic family, the Bellegardes. Several days later, Newman stops by the Tristram house only to find the visiting Claire, who politely invites him to call on her. When Newman stops by the Bellegarde home, a pleasant young man promises to go get Claire, but is checked by an imposing older figure who claims she is not at home.
Shortly thereafter, M. Nioche, Noémie's father, appears at Newman's hotel with his daughter's heavily varnished and framed picture. When the timid, bankrupt Nioche admits his fear that his beautiful daughter will come to a bad end, Newman offers to let her earn a modest dowry by painting. When he meets Noémie in the Louvre to commission the paintings, however, she tells him bluntly that she cannot paint and will only marry if she can do so very well. Mrs. Tristram encourages Newman to spend the summer traveling, promising that Claire will wait for his return. Newman spends a wonderful summer exploring ruins, monuments, cathedrals, and the countryside with his usual enthusiasm. On his return to Paris in the fall, Newman calls on Claire and finds her at home with her brother Valentin, the pleasant young man he met on the first visit. Newman is deeply drawn to Claire's presence, her peace, and her intense yet mild eyes. About a week later, Valentin calls on Newman at home. The two talk late into the night and soon become fast friends. Valentin explains to Newman that Claire was married at eighteen, against her will, to the disagreeable old Count de Cintré. Valentin tried to stop the wedding, but his mother, the Marquise and his brother, Urbain—the imposing older figure who barred Newman's first visit—coveted the Count's pedigree and fortune. When the Count died and his questionable business practices were exposed, Claire was so horrified that she withdrew her claim to his money. The Marquise and Urbain allowed this withdrawal on the condition that Claire obey them completely for ten years on every issue but marriage.
Newman tells Valentin that he would like to marry Claire. Valentin promises to help Newman's cause, out of both friendship and a spirit of mischief. The following day, Newman calls on Claire and finds her alone. He frankly details his love, his assets, and his desire to marry her. Fascinated but hesitant, Claire tells him she has decided not to marry, but agrees to get to know him if he promises not to speak of marriage for six months. Delighted by Newman's success, Valentin arranges an audience with the heads of the family—the forbidding Marquise and Urbain—later that week. On the appointed evening, after some painful small talk, Newman horrifies the assembled company with a long and candid speech about his poor adolescence and the makings of his fortune. When the others have left for a ball, Newman bluntly tells the Marquise that he would like to marry her daughter. After inquiring with equal frankness about his wealth, the Marquise grudgingly agrees to consider his proposal. Several days later, M. Nioche unexpectedly appears at Newman's hotel room, clearly worried about Noémie's antics. Newman decides to visit Noémie at the Louvre to discern the trouble. He encounters Valentin en route and brings him along. Valentin, completely charmed by Noémie and her ruthless, sublime ambition, resolves to pursue her. Shortly thereafter, Newman receives an invitation to dinner at the Bellegarde house. After dinner, Urbain confirms that the family has decided to accept Newman as a candidate for Claire's hand.
Over the next six weeks Newman comes often to the Bellegarde house, more than content to haunt Claire's rooms and attend her parties. One afternoon as he awaits Claire, Newman is approached by Mrs. Bread, the Bellegardes' old English maid, who secretly encourages him in his courtship. Meanwhile, the Bellegardes' long-lost cousin Lord Deepmere arrives in Paris. Upon the expiration of the six-month period of silence about marriage, Newman proposes to Claire again, and she accepts. The next day, Mrs. Bread warns Newman to lose no time in getting married. The Marquise is evidently displeased by the engagement, but agrees to throw an engagement ball. The following few days are the happiest in Newman's life, as he sees Claire every day, exchanging longing glances and tender words. Meanwhile, the Marquise and Urbain are away, taking Deepmere on a tour of Paris. On the night of the Bellegarde ball, Newman suffers endless introductions gladly and feels elated. He surprises first the Marquis and then Claire in heated discussions with Lord Deepmere, but thinks little of it. Afterwards, he and Claire exchange declarations of happiness. Shortly thereafter, Newman attends a performance of the opera Don Giovanni, and sees that several of his acquaintances are also there. During the second act, Valentin and Stanislas Kapp, who have both been sitting in Noémie's box, exchange insults and agree to a duel as a point of honor. Noémie is thrilled, knowing that being dueled over will do wonders for her social standing. Against Newman's protests, Valentin leaves for the duel, which is held just over the Swiss border.