The novel tells us about the tragic misunderstanding and culture clash that turned into drama a clearly romantic story. A young American named Winterbourne, who has lived in Europe for many years and has almost forgotten American customs and culture, comes to a small Swiss town of Vevey to see his aunt. In the hotel he accidentally meets the rich American family - the Millers - and is very surprised by their behaviour. The family consists of nine-year-old boy who looks very badly behaving and loud from the European point of view, his seemingly estranged and carefree mother and - what is much more important - his sister, named Daisy Miller. The family travels through Europe to Italy, in a company of their also European and quite restrained (or shall we say, prudish?) agent.
Daisy Miller stuns Winterbourne with her unkempt and cheerful behaviour and natural beauty. She is too free and relaxed in comparison with European girls, up to the point her behavior can be considered as unacceptable for a woman. She talks without any embarrassment to a stranger and captivates Winterbourne with her spontaneity. She omits all the necessary “small talk” part and openly talks about her family, her plans, her travel experience and her future - that does not include a happily married life, at least yet. Daisy really likes Europe very much and she wants to see as many touristic places as possible. The only thing that upsets her here is lack of socializing and parties woman are allowed to participate in.
Winterbourne is fascinated and puzzled: he never heard of young ladies talking about themselves like this. He tries to understand, what lies behind this strange behaviour: corruption or naivete? He finally finds the definition that satisfies him: a pretty silly American, and calms down a bit, just accepting Daisy the way she is. He finds out that she didn’t visit the castle of Chillon, but wants to do it very much. So, Winterbourne offers her to be her guide - but is immediately frightened that his offer might be misunderstood badly and adds that he will be happy to accompany Daisy and her mother. But Daisy doesn’t even understand why the situation was so embarrassing to Winterbourne. She is fine to go with him alone and enjoy the beauty of Chillon. Equally shocked and excited, the young man agrees, seeing their walk as a kind of forbidden fruit: breaking an incredibly attractive taboo.
Before the walk he talks to his aunt about Millers in general and Daisy in particular. He asks her to come with them to save the girl from bad gossips. But the woman says that she prefers to stay away from these vulgar and badly educated people. She is shocked that they treat their travelling agent as their close friend. But when Winterbourne’s aunt learns about the excessively free behaviour of Daisy and her desire to go to the Chillon castle in the company of man who is barely familiar to her, she outright refuses to get acquainted with Millers, no matter how charming Winterbourne considers Daisy.
In the evening Winterbourne meets Daisy in the garden. Despite it is very late, the girl comes alone and is very happy to meet him. Winterbourne is embarrassed: he doesn’t know how to tell a girl he likes that his aunt, whom he promised to invite, has a very low opinion of her. He quickly comes up with a plausible version of a terrible migraine that tortures his aunt, but Daisy immediately understands that it’s not the real cause. Nevertheless, she doesn’t care and is even glad that they can spend all the next day together, without any extra people. Winterbourne still doesn’t understand, whether she is truly indifferent or just lacks morals. Before they go, he insists on meeting Mrs. Miller. Winterbourne secretly fears that she will be very displeased with the behaviour of her daughter and will forbid her to go with him anywhere, but to his another surprise, Mrs. Miller takes the news calmly. Daisy casually introducts Winterbourne to her and says that they are going to visit Chillon castle together. Still her mother is fine with such shocking news!
But Daisy finds a way to embarrass even her mother. She wants Winterbourne to ride her on the boat right now, before they go. Now both Mrs. Miller and the travelling agent, who came to visit her, consider such behaviour indecent and provocative, but after a light quarrel and making everyone feel uncomfortable, she laughs and says that she was just teasing everyone. Then Daisy just goes home to sleep.
Winterbourne has never seen such behaviour before. If he could become more puzzled, he became. He sees her freedom as a series of the incomprehensible quirks, but still he is incredibly attracted to this savage girl. Two days later he comes to pick Daisy up and go to the castle of Chillon. He still feels like they are doing something risky and forbidden and expects the same attitude from Daisy, but the girl is absolutely calm and happy. They reach the castle and have a small stop there. Daisy chats with Winterbourne about everything in the world, admires him and his education. She also invites Winterbourne to travel with them to Italy and help her to educate her brother Randolph on their way, but that’s really too much for a reserved European man. Winterbourne replies that, unfortunately, he has other plans and soon he must return to Geneva. Daisy suggests that he has a girlfriend there and starts to openly tease him: cheerfully and tactlessly, saying that she would stop only if he promises to come to Rome in winter.
This is much easier to promise, because his aunt has a house in Rome and he has already received an invitation from her to visit her there. But it still doesn’t satisfy Daisy: she wants Winterbourne to come to Rome for her, not for his aunt. Finally, after the day spent together, Winterbourne returns Daisy to her home and goes to his aunt to tell about their walk. The aunt is shocked even more than he is and not in a positive way. She berates her nephew for wanting to introduce her to such a strange and shameless person. Winterbourne stays with her for some days more, not seeing Daisy again, and returns to Geneva, where he indeed has a girlfriend.
In late January Winterbourne arrives to Rome. The aunt, who is waiting for him, gladly informs him that the girl he was so excited about appears to be in a company of certain local gentlemen with refined manners and magnificent mustaches. Winterbourne tries to justify Daisy’s behaviour in the eyes of his aunt, assuring her that Daisy isn’t flirting with everyone, she is just naive, childlike and simple-minded, nothing more. But the aunt still thinks that the Millers are horrendously vulgar and their behaviour is unacceptable.
Despite Winterbourne believes in Daisy’s innocence, the information about the bearers of magnificent mustaches keeps him from visiting the girl immediately. Instead he goes to visit Mrs. Walker, a familiar American woman who was living in Switzerland most of the time. But on his way Winterbourne accidentally meets the Millers and Daisy berates him for not coming to see her. Winterbourne excuses, saying that he has just arrived. Daisy asks Mrs. Walker for permission to visit her this evening with her close friend Mr. Giovanelli - obviously one of the local gentlemen that seem to court her. Mrs. Walker is too polite to refuse. Daisy thanks for the invitation and goes for a walk to the local park, where Giovanelli is already waiting for her. Mrs. Walker reminds her that it is very indecent for the young girl to walk alone with a man and Daisy, tired of it, asks Winterbourne to accompany her.
In the park, Winterbourne, who is jealous, doesn’t want to leave them alone walking with them. To his another shock, Daisy is fine, talking equally freely with both men. She doesn’t even try to get rid of any one of them to spend more time with another. Again he is fascinated by such a combination of purity and shamelessness. Mrs. Walker, who believes that Daisy is ruining her reputation this way, comes after her to the park, but Daisy refuses to leave with her. She doesn’t see anything wrong in her behaviour and also doesn’t understand why she should sacrifice her freedom to social rituals. Winterbourne tries to convince Mrs. Walker that she is wrong and Daisy indeed doesn’t flirt with anyone, but the woman is adamant in her belief that Daisy is compromising herself, dancing all the evening with one partner, paying and accepting visits at 11 PM etc. She advises Winterbourne to forget Daisy to save at least his own reputation, but he refuses.
Three days later Winterbourne comes to the party organized by Mrs. Walker. Mrs. Miller and Daisy also arrive there, almost at midnight, and Giovanelli is with them. Winterbourne tries to mildly scold Daisy, saying that a young unmarried lady should not flirt so openly. Daisy ironically replies that when she will become an old married lady flirting would be even more inappropriate. She spends almost all the party with Giovanelli, in private. That is absolutely scandalous and the patience of Mrs. Walker comes to an end. When Daisy comes to her to say goodbye and thank for the party, Mrs. Walker just turns and leaves, ignoring her. Daisy is hurt and offended and Winterbourne, even despite he was also displeased with her behaviour, is upset to see her humiliated like this.
Later he often walks past the hotel where the Millers stay, but rarely finds them at home. He sees that Giovanelli is indeed a frequent visitor. The only way for him to understand such a behaviour is to assume that Daisy is in love with him. Winterbourne discusses this version with his aunt and she says that, probably, Giovanelli is a gigolo and the only thing he is interested in is Daisy’s dowry. No sane man wants to marry such a shameless girl, so it’s the only reason. After that talk, Winterbourne himself starts to doubt the purity of the girl and comes to the conclusion that her quirks are not so innocent.
He tries to find out if Daisy is engaged to Giovanelli by blatantly asking her mother. Mrs. Miller says that Daisy is not, but she isn’t sure. A shock again: the mother doesn’t know anything about the possible marriage of her daughter! Winterbourne can’t understand if Daisy deliberately teasing all the society or she sincerely doesn’t notice that everyone turned away from her.
A week later, Winterbourne goes for a walk late at night and wanders off to the Coliseum. Daisy is there, but with Giovanelli. Offended, Winterbourne decides to leave, but Daisy notices him and cheerfully calls him to join them. Suddenly, Winterbourne remembers how dangerous is to walk there at night, because the dampness of the Coliseum hosts lots of different and dangerous illnesses. Daisy may become very sick because of her recklessness. Winterbourne scolds Daisy and her companion for recklessness. Giovanelli tries to excuse, saying that he also was against this walk, but Daisy insisted. When Giovanelli walks away for a moment, Daisy asks Winterbourne whether he really believes that she and Giovanelli are engaged. Winterbourne answers that he doesn’t think it is important for him anymore, and the only thing he cares for is Daisy’s health. Daisy and Giovanelli leave, he promises to take her home.
Two days later Mrs. Miller tells Winterbourne that Daisy is dangerously ill. When she came to her senses briefly, she asked to tell Winterbourne that she is not engaged to Giovanelli and she does care about his opinion. Daisy also asked if Winterbourne remembers their trip to the castle of Chillon. A week later Daisy dies. At the funeral Giovanelli tells Winterbourne that he never met such a beautiful and kind being, pure innocent soul and a devoted friend. A friend! The heart of Winterbourne now is filled with pain and anger: for all this time he thought about Daisy much worse than she deserved.
In the following year he remembers Daisy a lot. His conscience torments Winterbourne, he thinks again and again that he was so unfair to her. She had her self-respect, but belonged to the different, much more opened culture. Finally he confesses to his aunt before returning to Geneva that their mistake was unavoidable. She is a European and he lived outside of America for too long.