Leona Samish, an American tourist, arrives in Venice on vacation and is overwhelmed by her first views of the city ("Someone Woke Up"). She finds a guide, a ten-year-old boy named Mauro, to lead her to the pensione where she will stay. En route, as Leona busily tries to find a good angle for a photograph, she falls into a canal.
At the pensione, Leona tries her primitive Italian on the owner, Signora Fioria, a down-to-earth, realistic woman. The other guests are all Americans. Signora Fioria tells them that of the various nationalities she hosts in her pensione, her favorite are the Americans (“This Week Americans”). The Americans currently staying at the pensione include Jennifer and Eddie Yaeger, an attractive young couple, and Mr. and Mrs. McIlhenny, a middle-aged couple. Leona, who is very sensitive about her single status, befriends everybody, serving them martinis and joining their chit-chat about travelling (“What Do We Do? We Fly!”). Soon, however, the others go out to have dinner, leaving Leona alone with her guide book.
The next day, Leona sees a beautiful eighteenth-century Venetian glass goblet in a shop. When she tells the shop owner, a handsome man named Renato Di Rossi, that she’d be willing to buy a pair of goblets, he promises to try to find another one. He then turns on the charm (“Someone Like You”), but Leona is suspicious. She thaws a little when he explains how to shop in Italy (“Bargaining”), but remains distant, something she regrets later that evening when she finds herself the only person alone in the piazza (“Here We Are Again”).
Her loneliness takes her back to Di Rossi’s shop the next morning, but he is not there. She buys the single goblet from his assistant, Vito. Returning to the pensione that afternoon with Mauro, she finds that Di Rossi has sent the mate for her goblet. He himself turns up and asks her for a date. Her joy is tempered by the suspicion that she might be taken for one of those wealthy American tourists, but Di Rossi manages to allay her fears. When the McIlhennys return to the pensione with a goblet that looks exactly like Leona’s and that they just watched being made especially for them, Di Rossi explains that all the goblets in Venice are designed the same way. Leona, however, remains unsure about going out with him (“Thinking”). Finally, she accepts.
That same evening Vito shows up at the pensione to tell Leona that his father, meaning Di Rossi, will be a little late for his date with Leona. Deeply dismayed at learning that Di Rossi is married (and did not tell her this), she breaks the appointment and goes off with Jennifer, whose husband has been flirting with Fioria. After his wife has left, Eddie stalls the consummation of the flirtation with the owner of the pensione by insisting on giving an English lesson (“No Understand”) to her maid, Giovanna.
Fioria, however, continues her pursuit of Eddie, and they go off to make love in a gondola. Leona sees them go and is shocked. When Di Rossi appears, she vents her frustrations on him and becomes even angrier when she learns that he is still with his wife but “lives outside.” Di Rossi accuses her of being naively romantic and unrealistically puritanical. He offers his affection and an affair for the time she will be in Venice (“Take the Moment”), and Leona accepts.
At the pensione that night, Jennifer, Fioria and Leona contemplate the moon (“Moon in My Window”). Jennifer is still trying to pretend there is nothing wrong with her marriage. Leona is wistful: although her evening with Di Rossi was nice, she had always met the right man, she would hear a waltz. And she didn’t with Di Rossi.
The next evening, while Leona is waiting for Di Rossi and fearing that he might not come, Eddie and Jennifer have another battle and then try to pretend everything is fine between them (“We’re Gonna Be All Right”). Di Rossi finally appears, late because he has bought Leona a garnet necklace. Leona, who has a passion for garnets, is overjoyed, and for the first time she hears a waltz (“Do I Hear a Waltz?”). When they return to the pensione the next morning, Di Rossi asks her not to return to America (“Stay”).
Leona wants to share her happiness and gives a party for the other guests at the pensione (“Perfectly Lovely Couple”). Suddenly Vito arrives and tells his father that the jeweler is waiting outside for the rest of the money for the necklace. Leona gives Di Rossi the amount needed, but her embarrassment turns to agony when Vito returns with some lire which the jeweler has said is Di Rossi’s commission for the sale. Leona refuses to believe Di Rossi’s shocked denial. She throws him out and proceeds to get drunk. Because she is hurt, she tries to hurt in turn and reveals the affair between Fioria and Eddie. The party ends in horror. Alone, Leona realizes the truth about herself.
The following day, all the guests are leaving. Di Rossi returns and tells Leona that her suspicions about him have destroyed his feeling for her. The only time she trusted him, he says, occurred when he gave her the necklace, “something you could touch, something that cost.” Leona sees her mistakes and would like to begin again, but Di Rossi, while wishing her well, says that cannot be. He can no longer feel about her as he did. They part, with a mix of affection and disappointment (“Thank You So Much”).
(Adapted from the synopsis included with the CD issue of the original Broadway cast recording.)