When dapper hotel magnate Ray Hunter arrives in Rome to finalize the purchase of the Regent Hotel, he is met by a throng of reporters and the dignified Maria Martelli, who is in the service of the Regent’s owner, Countess Alzani. After flirting with Maria during the drive, Ray arrives at the countess’ mansion, where the elder matron immediately accuses the “bachelor with ten thousand bedrooms” of running his hotels like “assembly lines.” After Ray assures her that he will retain her current employees, the countess closes the deal. During the drive back to the city, Maria mocks Ray about his “buying game.” Instead of rebuking her, Ray appreciates her frankness, causing Maria to apologize by offering to be his translator that afternoon during staff introductions. When Maria stops briefly at her home, Ray meets Maria’s youngest sister, the eighteen-year-old Nina, and her father Papa Vittorio. With her father accompanying her on piano, Nina sings Ray a romantic Italian number, brazenly flirting with the bachelor. Ray shows off his own musical talent singing the same song in English. Later, after a tour of the luxurious hotel, Ray invites Maria to dinner and whisks her onto the dance floor, where he serenades her. Soon after, Maria’s suitor Anton, an impoverished Polish count and sculptor, joins them at their table and lavishes attention on Maria, who, he explains, is a sculptor with whom he shares his studio. After a disappointed Ray hastily leaves the couple, Anton insinuates that contact with the millionaire will help his own career. At the hotel, Ray’s pilot Mike Clark notices sexy Nina, who works as the hotel stenographer, and is immediately smitten after a brief flirtation. Later in the evening, Nina attempts to seduce Ray in his room under the guise of offering dictation services. Succumbing to the young woman’s advances, Ray takes her on a flying tour over Rome that evening, where he sings to her. Swooning from his attentions and the champagne, Nina falls into Ray’s arms insisting that she wants to marry him. Ray returns with Nina to the Martelli home that evening to ask for her father’s consent. Papa refuses, scolds Nina for her reckless behavior and explains to Ray that family tradition dictates that all the older sisters must marry before Nina is allowed to wed. Later, when Nina announces her engagement to Maria and sings a few bars of Ray’s serenade, Maria bitterly comments that the fickle man has a “limited musical repertoire.” Determined to overcome her father’s objection, Ray calls company associates Tom Crandall and Bob Dudley in the United States and orders them to fly to Rome under the pretense of important business. Wanting to set a romantic tone for Tom and Bob’s introduction to the remaining Martelli sisters, Diana and Anna, Ray requests that a grand party be held the following evening at the hotel. Meanwhile, Mike requests Nina’s services in his room and dictates an autobiographical letter as a romantic ploy, but she shuns him. Now needing to marry off only Maria, Ray visits Anton’s studio, where he buys an abstract sculpture for cash and commissions more for his hotels. Hours later, Anton excitedly reports his sales to Maria and proposes, but Maria refuses him, then goes to the hotel to tell Ray that she disapproves of his “instant marriages.” Ray graciously apologizes, which prompts Maria to offer to dissuade her father from following the outdated family tradition. Ray is so overjoyed that he kisses her, leaving Maria speechless. Meanwhile, when the relentless Mike finds Nina at nearby café and professes his love, Nina reluctantly admits that she has feelings for him. At the party that night, Ray’s plan appears to be working when he spots Bob and Tom happily dancing with Diana and Anna. When he discovers Maria has left early, Ray finds her at the studio, where she tells him that she resents his commissions as a way of buying her a husband and attaining Nina for himself. Although he admits his mistake, Maria continues to berate him. Ray impulsively embraces and kisses her, causing Maria to flee. Back at the party, Mike, knowing that Nina has yet to break up with Ray, drowns his disappointment with martinis and sends Nina away when she approaches him. In the ballroom, Papa, with a little encouragement from the romantic countess, announces Ray and Nina’s engagement to the crowd. Much later in his hotel room, Ray admits to his valet Arthur that he is engaged to the wrong woman. When Arthur suggests they leave town, Ray complains that millionaires are not free from social constraints. Arthur chides that the “poor unhappy millionaire” should give his problems to his valet. Meanwhile, a despondent and confused Maria finally agrees to marry Anton. Early the next morning, after Bob and Tom announce to Ray that they have proposed to Diana and Anna, Anton reveals that Maria has accepted his proposal. Soon after, Mike reports that he is quitting because of his love for Ray’s fiancée. Ray, sensing that the competition might resolve his dilemma, urges Mike to fight for Nina’s hand. At the Martelli house, Anton, Bob and Tom parade into Papa’s kitchen to ask for his daughters’ hands in marriage. When Mike shows up moments later for Nina’s hand, Papa demands an explanation from his daughters. While the women battle out the misunderstanding in Italian, Ray takes advantage of Anton’s greed, offering him a job in Bombay that requires that he be bachelor, which Anton eagerly accepts. Days later the four sisters are married, Maria to Ray, Nina to Mike, Bob and Tom to Diana and Anna, while the countess and Papa debate on who finally decided to marry whom.