Winterbourne, a young American who has been living in Europe for many years and has managed to break the habit of American customs, comes to the small Swiss town of Vevey to see his aunt. At the hotel, he accidentally meets a wealthy American Miller family - a nine-year-old boy, his older sister and their mother. They travel around Europe accompanied by their agent and are going to go to Italy. The girl - Daisy Miller - amazes Winterbourne with her beauty, as well as free and laid-back behavior, which is not accepted in Europe. Without embarrassment, she talks to a stranger and captivates Winterbourne with her spontaneity. She talks about her family, about traveling in the company of mother and brother, about future plans. She loves Europe and wants to see as many attractions as possible. The only thing that upsets her is the lack of society, they traveled to America much more often, and she often visited male society. Winterbourne is at once fascinated and puzzled; he had never heard young girls say such things about themselves. He is trying to understand what is behind this strange behavior from a generally accepted point of view? He finds Daisy's definition: a pretty windy American, and rejoices that he has found a good formula.

Having found out that the girl has not been to Chillon Castle yet and really wants to visit him, Winterborn offers to accompany her. Frightened by his own insolence, he adds that he will be happy to accompany her and her mother, but neither his insolence nor his reverence seem to make the slightest impression on the girl. Finally bewildered by her equanimity, Winterbourne enjoys the opportunity to make this excursion together with Daisy and promises to introduce the girl to her aunt. But when he speaks with his stiff relative about the Miller family, she says that she prefers to stay away from these vulgar and ill-mannered people. She is shocked that they treat their traveling agent as a close friend, she is outraged by Daisy's free behavior, and when she finds out that the girl is going to Chillon Castle in the company of Winterbourne, who barely knows her, she flatly refuses to get acquainted with the Millers.

In the evening, Winterbourne meets Daisy in the garden. Despite the late hour, the girl walks alone and enjoys meeting. Winterbourne is confused: he does not know how to tell a girl about her aunt’s refusal to meet her. He refers to a migraine tormenting her, but Daisy immediately realizes that this is not the case. However, such legibility in dating does not upset her at all, Winterbourne still can not understand whether a girl shows ostentatious or true indifference. They meet Mrs. Miller, and the girl calmly introduces her to Winterbourne, after which she placidly announces that she is going to visit Chillon Castle in his company. Winterbourne fears the displeasure of Mrs. Miller, but she takes the news quite calmly. Daisy says she wants Winterbourne to ride her on a boat right now. An agent of her parents who approached them and Mrs. Miller believe that it is indecent, but they do not dare to argue with Daisy. Teasing everyone a little, she says: “This is what I need - so that someone gets a little worried!” - and goes home to sleep.

Winterbourne is puzzled and ponders over obscure quirks and unceremonious girls. Two days later, he goes with Daisy to Chillon Castle. In his opinion, there is something courageous, risky in this escapade of them, he expects a similar attitude from Daisy, meanwhile, the girl is completely calm. In Chillon Castle, she talks with Winterbourne about everything in the world, admires his education. She invites Winterbourne to go with them to Italy and take on the training of her brother Randolph, and she is very upset to hear that he has other things to do and that he will not only not be able to go with them to Italy, but in a day or two he must return to To Geneva. Daisy assumes that there is a “charmer” waiting for Winterbourne and, with an amazing mixture of simple-mindedness and tactlessness, begins to shower him with ridicule, saying that he will stop teasing him only if he promises her to come to Rome in the winter. Winterborn is ready to promise her this: his aunt rented a house in Rome, and he has already received an invitation to visit her there. But Daisy is unhappy: she wants Winterbourne to come to Rome not for her aunt, but for her. When he tells his aunt that Daisy went with him to Chillon Castle, she exclaims: “And you were going to introduce me to this person!”

In late January, Winterbourne arrives in Rome. My aunt informs him that Daisy appears in the company of a certain gentleman with exquisite manners and a magnificent mustache, which causes a lot of sense. Winterbourne is trying to justify Daisy in the eyes of her aunt, assuring her that she is simple-minded and ignorant, nothing more. But the aunt considers the Millers terribly vulgar, and their behavior reprehensible. The information that Daisy is surrounded by “owners of a magnificent mustache” keeps Winterbourne from an immediate visit to her. He goes to visit Mrs. Walker, an American friend who lives in Switzerland most of the time, and she suddenly meets the Miller family. Daisy rebukes him for not coming to see her. Winterbourne makes excuses, saying that he arrived only the day before. Daisy asks Mrs. Walker for permission to come to her for an evening with her close friend Mr. Giovanelli. Mrs. Walker does not dare to refuse her. Daisy is going to walk in the park on Pinchio, where Giovanelli is already waiting for her. Mrs. Walker notices her that it is indecent for a young girl to go there alone, and Daisy asks Winterbourne to accompany her.

In the park, Winterbourne does not want to leave young people together and walks with them, surprised that Daisy is not trying to get rid of him. The combination of shamelessness and purity in a girl is a mystery to him. Mrs. Walker, believing that Daisy was ruining her reputation, came to the park for her, but Daisy resolutely refused to leave her companions and sit in her carriage. She does not see anything wrong in her behavior and does not understand why she should sacrifice her freedom to decency. Winterbourne is trying to convince Mrs. Walker that she is wrong, but Mrs. Walker believes that Daisy compromises herself by dancing all night with one partner, hosting guests at 11 p.m., etc. She advises Winterbourne to stop meeting Daisy, but Winterbourne refuses . Three days later, Winterbourne arrives at Mrs. Walker's reception. There he meets Mrs. Miller, and Daisy arrives at twelve o'clock in the company of Giovanelli. Winterbourne is trying to reason with Daisy, explaining to her that the young girl should not be flirting with young people. “And it seemed to me that flirting is more to face unmarried girls than married ladies,” Daisy retorts. She quietly retires with Giovanelli in the window niche of the next room and spends there almost the whole evening. Mrs. Walker finally decides to show firmness, and when Daisy comes to her to say goodbye, she turns her back on the girl. Daisy is amazed and hurt, Winterbourne's heart is contracting at the sight of this scene. He often goes to the hotel, where the Millers stayed, but rarely finds them at home, and if he does, then in the company of Giovanelli. He tries to understand if Daisy is in love, and discusses his assumption with his aunt. Aunt quite admits the idea of ​​a marriage between her and Giovanelli, who seems to her a dowry hunter. Winterbourne begins to doubt Daisy's cleanliness and is inclined to think that her folly is not so innocent. He is trying to find out if Daisy is engaged to Giovanelli. Her mother says no, however, she herself is not sure about it. Daisy during a casual meeting tells Winterbourne that she is engaged, but immediately refuses her words. Winterbourne cannot understand in any way whether Daisy does not notice that the whole society has turned her back on her, or, on the contrary, she consciously challenges others.

A week later, Winterbourne sets off for a walk late in the evening and wanders to the Coliseum, where he meets Daisy with Giovanelli. He decides to leave, but Daisy calls out to him. And here Winterbourne recalls how dangerous it is to walk here, because the air is full of poisonous miasms, and Daisy can get a fever. He scolds Daisy and her companion for imprudence; Giovanelli makes excuses: he tried to dissuade his companion, but to no avail. Seizing the moment, Daisy asks if Winterbourne believed that she and Giovanelli were engaged. Winterbourne responds evasively and concludes by saying that now it seems to him that this is not so important. Daisy leaves home accompanied by Giovanelli, and Winterbourne finds out in two days that she is dangerously ill. Mrs. Miller tells him that, waking up from delirium, Daisy asked to tell him that she was not engaged to Giovanelli, and ask if he remembers the trip to Chillon Castle. A week later, Daisy dies. At the funeral, Giovanelli tells Winterbourne that he had never met such a beautiful and kind girl, such a pure innocent soul. Winterbourne's heart shrinks in pain and anger. The following year, Winterbourne thinks a lot about Daisy, his conscience torments him because he was unfair to her. In fact, she really appreciated self-respect. He confesses to his aunt: “I could not help but make a mistake. I have lived too long abroad. ”