Lucille Lombardi, a beautiful Italian businesswoman, discovers that her boyfriend and marketing director, Julien Auchard, has bankrupted her family business, cheated her out of her wealth, and left her penniless. Shocked by the betrayal, the loss of her villa in Nice, and feeling that all is lost, she decides to sell her jewelry and binge on champagne and caviar before committing suicide. Her binge renders her intoxicated and leaves her daydreaming about revenge. At first she plans to leave Julien Auchard a note blaming him for her death, but realizing it would have little effect on him, she decides that revenge is the only course—that she must kill Julien Auchard before ending her own life. Knowing that Julien travels to Paris every Friday, Lucille decides to hold off on suicide for one week until she has a chance to kill the man who ruined her life.
After arriving in Paris, Lucille buys an Austin Princess luxury car and sets about planning her revenge while continuing her lavish spending on designer clothing and food. Uncomfortable being alone, she invites a stranger named François, a marine salvage expert, to have a romantic lunch with her at the Eiffel Tower. When Lucille reveals her intentions to end her life later that week, François shows genuine concern for her and states that he will not allow it—that he'll not leave her side. Lucille manages to elude him after lunch and he is unable to follow. In the coming days, François desperately tries to locate her as she continues her spending spree on fine clothes and expensive food and champagne while waiting for her ex-boyfriend to arrive in Paris.
While posing as a Swiss journalist, Lucille becomes entangled with a New York News correspondent named John Bert, a shady Spaniard named Alberto de Villalonga, and the drug-addled manager, Tom Sturges, of an English rock group named The Timothys who just appeared at London's Royal Albert Hall. She goes on a series of dates, continuing her extravagant spending during her final days. Meanwhile, François continues his desperate search for the woman he believes will kill herself on Friday. After receiving no help from the police, he tracks down all the Austin Princess owners in Paris, thinking it will lead him to Lucille. Despairing on not finding her, he resigns himself to his work, which involves a lucrative new salvage operation in Venezuela that will make him wealthy (from the shady Spaniard Alberto as it turns out).
On Thursday night, Lucille wanders the streets of Paris alone. A man approaches her, mistaking her for a prostitute, and she goes back to his place to have sex, later giving away the 300 francs she was paid. On Friday, Lucille meets Julien at the Paris-Orly Airport pretending she has a wealthy investor who can buy back the company that Julien now owns. Interested in the deal, Julien accompanies her to her hotel room where she pulls her gun, demanding that she accompany him to his appointment in Chantilly. Intending to kill them both in an auto accident, Lucille has second thoughts just as they are about to crash into an electrical pole. > You disgust me so much that it will save your life, <br/> as she tells him, and she leaves at the roadside and drives away.
Back in Paris, François spots Lucille's Austin Princess by chance and follows her to the Eiffel Tower, where she intends to end her life. At the top, Lucille considers jumping, but something prevents her. When François arrives at the top, he finds her eating dessert in the restaurant where they enjoyed their romantic lunch, and they smile at each other.
