Maria Williams, Maggie McNamara, arrives in Rome to take over at the United States Distribution Agency and is greeted by Anita Hutchins, Jean Peters, the woman she is replacing. They travel to the Villa Eden, where Anita shares the home with Frances, Dorothy McGuire, the longtime secretary of American author John Frederick Shadwell, an expatriate living in Rome. On the way into town they stop at the Trevi Fountain. Frances and Anita explain the legend that if you throw a coin and make a wish to return to Rome, the wish just might come true; Maria and Frances toss coins, while Anita, who plans to return to the United States to marry, declines.
Anita takes Maria to the agency and introduces her to Georgio Bianchi, a translator. Maria senses that Anita and Georgio are attracted to each other, though Anita insists that American and Italian staffers are not allowed to fraternize. Later that evening at a party, Maria becomes smitten with the dashing Prince Dino di Cessi, a reputation-filled womanizer who often ferries lovers to Venice for romantic escapades. Dino charms Maria and urges her to ignore the gossip surrounding him.
Walking home, Anita confesses that she has no fiancé but believes her best chance of marrying well is in the United States, since wealthy Italian men rarely consider secretaries, and those who do are not rich. They later encounter Georgio, who invites Anita to a celebration at his family’s country farm the next day. Anita reluctantly agrees and they head into the morning light with a mixture of excitement and uncertainty.
The next morning, as Georgio picks Anita up in his cousin’s dilapidated truck, they are spotted by Anita’s boss, Burgoyne, Howard St. John. On Georgio’s family farm, he shares his dream of becoming a lawyer despite poverty, and the two secretly kiss. Meanwhile, back at the apartment, Dino asks Maria to accompany him to Venice. To keep his respect, Maria arranges for Frances to chaperone them—much to Dino’s disappointment.
At the agency on Monday, Burgoyne questions Maria about Anita’s weekend with Georgio, and while Maria maintains that Anita did nothing wrong, Burgoyne assumes an affair has begun and fires Georgio. Anita blames Maria for betraying her confidence and insists on moving out. She visits Georgio, worried that she may have jeopardized his chances of becoming a lawyer; Georgio has no regrets.
Determined to win Dino’s affection, Maria gathers information about his interests—his taste in modern art, his preferred foods and wines—and even fabricates a detail about being “three-quarters Italian.” Intrigued by their shared interests, Dino introduces Maria to his mother, Principessa, who approves of the match. Dino confides that his mother is the only woman he has ever fully trusted, and Maria reveals her deception, which infuriates him.
Frances returns home, weighed down by guilt and the fear of becoming an old maid in a foreign land, while Maria awaits news about Dino. The next day, Shadwell, who has learned he is terminal, ends his engagement to Frances and contemplates a medical trip to the United States. After securing the truth from his doctor, Frances follows Shadwell to a cafe, where they argue and reconcile over his decision to pursue treatment.
Shadwell announces that he will leave for the United States, where he plans to marry Frances. Using reverse psychology, he suggests to Dino that he should pursue his feelings for Maria. With the plans in motion, Anita and Maria prepare to depart Rome, and Frances arranges a meeting at the Trevi Fountain.
At Trevi, the fountain is momentarily emptied for cleaning but then springs to life again as Frances joins Shadwell. Dino and Giorgio arrive, and the lovers embrace their partners, while Frances and Shadwell stand together, content to admire the fountain as the city hums around them. The story closes on a hopeful note, with two couples choosing love and partnership against the odds, set against the timeless charm of Rome.
