In a Swiss resort, Winterborne meets a pretty young American girl who seems to have no qualms about talking to strangers. During the course of their conversation, she mentions her desire to visit the castle across the lake. Winterborne declares that he would be delighted to accompany her.
A few days later, Daisy introduces him to her mother, and Winterborne fears that Mrs. Miller will deeply disapprove of his invitation. Instead, Mrs. Miller readily agrees as long as she does not have to go along. That night Daisy suggests a boat ride on the lake. Even though it would be improper, Daisy insists, but she suddenly changes her mind on learning that her brother is in bed. Winterborne is perplexed and confused by her actions.
Winterborne is aware that it was highly indiscreet for Daisy to go with him to the castle, but he is so charmed and pleased by her spontaneity and gaiety that he is willing to overlook everything else. Furthermore, he is convinced she was acting with perfect innocence.
Winterborne wants to introduce Daisy to his aunt, a Mrs. Costello, but this elderly lady has heard enough about the young American girl to think her common and vulgar, and consequently, refuses to meet her.
During the visit to the castle, Daisy learns that Winterborne has to leave the next day. After teasing him about being under the influence of some woman, she makes him promise to visit her in Rome that winter.
Some months later, Winterborne does go to Rome and immediately hears that Miss Daisy Miller is being "talked about." She is accused of picking up strange men and being seen with them in indiscreet places. At the house of a mutual friend, Mrs. Walker, Daisy meets and teases Winterborne again. Soon she mentions that she is going for a walk in order to meet a Mr. Giovanelli. Mrs. Walker is shocked and tries to tell Daisy how improper it would be to be seen walking the streets. Daisy solves this by asking Winterborne to accompany her.
After Daisy meets her companion, the three of them stroll about for a while. In a few minutes, Mrs. Walker drives up in her carriage and tries to convince Daisy to come with her. She lets the girl know how improper it is to be seen walking along the street with a man. Daisy thinks that if what she is doing is improper, then she is completely improper and asks the others to forget about her.
Later, at a party given by Mrs. Walker, Daisy offends her hostess by coming very late with her Italian friend. When Daisy leaves, Mrs. Walker snubs her and later tells Winterborne that Daisy will never again be allowed at her home.
For some time, Winterborne hears additional stories about Daisy, but he still maintains that she is an innocent but impetuous girl. He even tries to warn her about her indiscretions, but she is unconcerned. Winterborne continues to believe in Daisy's innocence until he passes by the Colosseum late one night. He enters to observe the arena and accidentally sees Daisy with her Italian friend. Then he realizes that she is not a young lady that a gentleman need be respectful to.
Winterborne advises Daisy to leave immediately, and he questions the Italian's intentions in bringing her there so late. A few days after this, Daisy catches the Roman fever, which causes her death. Three times during a period of consciousness, Daisy sent Winterborne a message that he could only interpret at a later date. He realized that Daisy was a very innocent girl who would have welcomed someone's esteem.
Note to the reader: Henry James revised almost all of his work for a final edition. Therefore, sometimes Daisy Miller appears with four sections, as is found in the following analysis. But it is just as possible to find it divided in only two sections. In this division, Section 1 combines the first two sections, that is, the episodes that take place in Switzerland, and Section 2 handles the Italian episodes.