In the early 1950s, young American secretary Maria Williams arrives in Rome to work at the U.S. Distribution Agency. She is greeted by Anita Hutchins, who she is replacing at the agency, and taken to the villa Anita shares with Miss Frances, the longtime secretary of noted American expatriate author John Frederick Shadwell. The three women then drive into town and along the way, stop at the famous Trevi Fountain. Frances and Anita relate the legend that if Maria throws a coin in the fountain and makes a wish to return to Rome, she will. Maria wishes to remain in Rome for a year, while Frances wishes for another year of contentment. Anita, who is returning to the U.S. to marry, declines to make a wish. While Frances then goes to Shadwell's lavish villa, Anita takes Maria to the agency and introduces her to their boss, Mr. Burgoyne. Anita also introduces Maria to Giorgio Bianchi, a translator, and although Maria senses that Anita and Giorgio are attracted to one another, Anita states that the agency forbids its American and Italian employees to fraternize. At a party that evening, Maria is dazzled by the handsome Prince Dino di Cessi, despite Frances and Anita's warning that he is a notorious womanizer, whose girl friends become known as "Venice girls" after he takes them to Venice for romantic rendezvouses. Dino charms Maria and tells her to ignore the bad things she has heard about him, and later, as Anita and Maria walk home, Anita admits that she has no fiancé but hopes to have a better chance of finding a husband in America. Anita explains that wealthy Italian men are not interested in mere secretaries, and that the men who are interested in them are too poor to marry. As they are walking, the women are pestered by several men and are rescued from their pursuers by Giorgio, who then asks Anita to go with him the next day to his family's country farm to attend a celebration. Anita reluctantly agrees, although she will be breaking agency rules, and the next morning, Giorgio picks her up in his cousin's delapitated truck. On their way out of town, they are spotted by Burgoyne and his wife, who are suspicious about their being together. Back at the apartment, Dino calls for Maria and asks if she will accompany him to Venice, and Maria, who desires to see Venice but not lose Dino's respect, arranges for Frances to chaperon them. On Giorgio's family farm, Giorgio tells Anita that he hopes to become a lawyer, despite his poverty. Anita then climbs into the brake-less truck and is almost killed, and after Giorgio rescues her, the breathless couple gives into their attraction and kisses. On Monday, Burgoyne questions Maria about Anita's weekend with Giorgio, and although she maintains that Anita did nothing wrong, Maria tells Burgoyne that Anita is not really engaged, and Burgoyne assumes that she is having an illicit affair with Giorgio. Mrs. Burgoyne tries to calm her husband that night, telling him "even nice girls are human," but the next morning, Burgoyne fires Giorgio. When she finds out, Anita yells at Maria for betraying her confidences and insists on moving out of their apartment until she leaves Italy. Anita then visits Giorgio, who does not regret their time together, although Anita is distraught that she may have ruined his chances of becoming a lawyer. Giorgio, who wants to marry Anita, ruefully wishes that he could propose, and Anita tells him the truth about her "fiancé." Meanwhile, desperate to help, Maria asks Frances to persuade Shadwell to help to restore Giorgio's job, after which Frances coaches Maria on art terms, and Maria intrigues Dino with her supposed deep love of modern art. Marie lies, telling Dino that she is three-quarters Italian, and then systematically gathers information about his likes and dislikes. Beguiled by how much he apparently has in common with Maria, Dino introduces her to his mother, the Principessa, who expresses her approval. Dino then confides in Maria that she is the only girl friend who he has ever completely trusted, and the heartsick Maria confesses her subterfuge, even showing Dino the dossiér she has compiled on him. Later, Frances meets with Anita, who admits that she and Giorgio are in love but have decided not to marry because he is too poor to support a family and continue his studies. Frances then goes home to comfort the guilt-stricken Maria, who is also determined to leave Rome because Dino has not contacted her since her admission. Frances states that she is glad she is no longer young and susceptible to romance, but the next morning, suddenly announces to Shadwell that she is returning to the U.S. Shadwell is bewildered, and Frances explains that she does not want to wind up an old maid in a foreign country. Shadwell, unaware that Frances has been deeply in love with him for fifteen years, offers her a marriage of convenience, based on mutual respect, and, eager to be with him under any circumstances, Frances accepts. Anita and Maria, who have reconciled, are thrilled by Frances' news, but the next day, unknown to Frances, Shadwell learns that he is terminally ill and has less than a year to live unless he goes to America for experimental treatment. When Shadwell returns to his villa, he coldly tells Frances that he made a mistake and releases her from their engagement, telling her that he will be leaving for Capri immediately. After Shadwell leaves, Frances receives a call from his doctor and learns the truth, then follows Shadwell to a café, where she proceeds to match him drink for drink while bickering about whether he should pursue treatment. Completely drunk, Frances climbs into a nearby fountain and sobs about her life and the predicaments of her friends, and after Shadwell takes her back to the villa and tucks her in, he goes to see Dino. At the di Cessi palace, Shadwell tells Dino that he is leaving tomorrow for the U.S., where he will marry Frances, and uses reverse psychology to provoke Dino into realizing that he loves Maria. Shadwell then visits Burgoyne, and the next day, after Anita and Maria are packed and ready to leave, Frances telephones and asks to meet them at the Trevi Fountain. Upon their arrival, Maria and Anita are dismayed to see that the fountain has been emptied for cleaning and Maria declares that it is a fraud. After Frances joins them, however, the water springs up again and the women are thrilled by its beauty. Dino and Giorgio then arrive, and as the men embrace their ecstatic girl friends, Frances is joined by Shadwell, and they happily admire the fountain, which has proved lucky after all.