Mo Alexander, a spunky horticulturist from St. Louis, Missouri, has agreed to help her friend Marcia chaperone a student group on a summer tour across Eastern Europe and Russia. However, during their layover in Paris, France, Mo misses the connecting flight to Warsaw, Poland. In need of place to stay in Paris until her travel is rebooked, Mo takes a taxi to the home of her old college friend, Chantal. In the hallway of the elegant apartment building, she encounters Chantal’s next-door neighbor, a suave banker named Xavier de La Pérouse, who informs her that Chantal is away for the summer. Tired of trying to communicate in French and soaking wet from the rain, Mo hopes there is a hotel nearby. Xavier, who speaks perfect English, offers his umbrella and walks her to a hotel around the corner. Before saying goodbye, she tells him that he has the most beautiful eyes. Later that evening, Xavier unexpectedly arrives at her hotel room with an apartment key, stating that he contacted Chantal and she happily agreed to let Mo stay. He also invites her to dinner, but the evening becomes awkward when Xavier implies that Mo is dressed too casually for a fancy restaurant. Although Mo is annoyed and walks away, she cannot resist the Frenchman’s charm when he offers to cook her spaghetti instead. At his apartment, Mo admires a photograph of Xavier’s two young children and his stylish wife Isabelle, who are on summer vacation. The following day, Mo consults with a travel agent and learns she must wait at least a week for visa updates before she can rendezvous with Marcia’s group. Meanwhile, Mo accepts another dinner invitation from Xavier and buys a new dress for the occasion. She enjoys the evening, but when the Frenchman tries to kiss her, she rebuffs him, reminding him that he is married. Xavier is surprised by her reaction, while Mo disapproves of “French rules” in which accepting a dinner invitation implies sex. Before saying goodnight, however, the two reach an understanding, and Mo thanks him for a wonderful evening. At the office, Xavier remains preoccupied by the American and tries to telephone her between his appointments, but she is busy playing baseball in the park with Andrew, a classical musician whom she met at the travel agency. That evening, Xavier meets Mo at Andrew’s concert, but he feels like an outsider when Mo and Andrew go to a discotheque after the performance. He returns to the apartment alone and pretends not to be jealous when Andrew escorts Mo home. However, as soon as Andrew leaves, Mo knocks on Xavier’s door and embraces him. Initially, she appears hesitant about being intimate, and Xavier accuses her of being a tease. She replies by passionately kissing him, and the two make love. In the morning, Xavier packs for a business trip. He tells Mo that he might be back as early as tomorrow night, but she is reluctant to wait for him after accepting an invitation to visit Rome, Italy. Regretfully, they say goodbye. However, as Xavier drives away and Mo leaves for her trip, they both change their minds and return to the apartment building. Once again, they encounter each other in the hallway, and Xavier asks Mo to stay with him until September. As the two embark on a love affair, they lounge in the apartment, drink wine, discuss cultural differences, and explore Paris. After friends of his wife spot Xavier kissing Mo, the couple escapes from the city to visit the country home of Xavier’s colleague Philip. Xavier mentions that Philip and his wife Sylvia are not friends of Isabelle. While attending a dance in the local village, Mo asks Xavier whether he loves his wife. Xavier admits that he may not love Isabelle, but they are both committed to the marriage. He also confesses that he has a mistress named Nathalie, whom he has seen on and off for the past three years. While Xavier describes the arrangement as “diplomatic,” Mo strongly disapproves and resents being his convenient summer fling. The next day, as Xavier and Philip return to Paris for business, Mo remains at the country house with Sylvia. When one of Sylvia’s young children is injured while jumping in the lake, the two women rush her to a hospital with Mo precariously speeding through traffic. By the time Philip and Xavier hear the news and arrive at the hospital, the doctor reports the child will be fine, and Xavier embraces Mo. Back in Paris, Mo and Xavier comfort each other after making love, and she tells him their three weeks together has felt like a lifetime. However, as September approaches, Xavier appears indifferent toward Mo. After Nathalie unexpectedly arrives at the apartment building, Mo books her flight back to Missouri and moves into the hotel around the corner for the remainder of her stay. On her last night in Paris, she takes a boat tour along the Seine River, but remains preoccupied by thoughts of Xavier. When she returns to the hotel, Xavier is waiting for her. He confesses he recently saw Nathalie, but did not make love to her. As Xavier and Mo reconcile and spend the night together, Xavier declares his love and asks Mo to stay in Paris. The next day, the affectionate twosome make plans to cook dinner as they leave the hotel. Mo offers to pick up bread, while Xavier returns to the apartment with her luggage. When Mo arrives and calls out to Xavier, she encounters his wife, who has unexpectedly returned from vacation. Realizing that Mo is Xavier’s mistress, Isabelle insinuates that she and her husband are back together. Mo leaves for the airport. Meanwhile, Isabelle reaches for her husband’s hand to encourage him to stay, but he runs after Mo, who has departed in a taxi. He follows her to the airport and fights through the crowds to catch her attention, but she does not notice him. After buying an airline ticket in order to pass through airport security, Xavier sees Mo descending on an escalator. As guards detain him, he yells out her name. She turns around and runs to embrace him.