In early spring, Winterbourne encounters Daisy and Giovanelli at the Palace of the Caesars. When Giovanelli leaves them alone for a moment, Daisy accuses Winterbourne of judging her relationship with Giovanelli. Winterbourne responds that everyone judges her. She asks why he doesn’t defend her, and he tells her he does and that he informs people of her mother’s belief that she and Giovanelli are engaged. Daisy says that they are engaged, and then, suggesting that Winterbourne doubts her, she says they are not.

One night, on his way home from a dinner party, Winterbourne decides to look at the Coliseum by moonlight and is shocked to discover Daisy there with Giovanelli. The two are standing together at the base of the great cross in the center. Winterbourne decides then and there that Daisy is not the kind of young woman with whom he needs to concern himself. He feels relieved and also angry with himself for having spent so much time trying to figure out how he should think about Daisy.

Still, Winterbourne cannot bring himself to leave the Coliseum without warning Daisy of the danger in which she has placed herself, since the ancient arena is well known as a breeding ground for malaria. He goes forward and asks sharply how long they have been sitting there. “All evening,” Daisy says gaily.

Winterbourne suggests they leave immediately and advises Daisy to take some pills that she says Eugenio can give her. When Giovanelli goes for a carriage, Daisy asks whether Winterbourne believed her the other day when she said she was engaged to Giovanelli. Winterbourne says it doesn’t matter what he believed. Daisy asks what he believes now, and he says he believes “it makes very little difference” whether she is engaged or not.

Within days, news reaches Winterbourne that Daisy is gravely ill. Mrs. Miller, who proves a tireless and devoted nurse, tells Winterbourne on one of the occasions when he visits that Giovanelli has not come near them since Daisy fell ill. She also passes on a message that Daisy, in one of her lucid moments, asked her to give to Winterbourne. The note states that she was never engaged to Giovanelli and that she wonders if he remembers the time they visited that castle in Switzerland.

A week later, Daisy dies and is buried in the famous Protestant Cemetery in Rome. At her funeral, Giovanelli tells Winterbourne that Daisy was “the most beautiful” and “the most amiable” young lady he ever saw. He adds, “She was also the most innocent.” Winterbourne asks why in the world Giovanelli took her to the Coliseum that night. “If she had lived I should have got nothing,” Giovanelli says, meaning that Daisy would never have married him.

After the funeral, Winterbourne leaves Rome, but he continues to think of Daisy and her “mystifying manners.” The next summer, while visiting his aunt again in Vevey, he tells her that he did Daisy an injustice. He says that before she died she sent him a message, the import of which he didn’t understand at the time, though he does now: she cared what he thought of her after all. Mrs. Costello wonders whether Daisy was trying to convey in her message that she would have returned Winterbourne’s “affection.” Winterbourne reminds his aunt that she had predicted he would make a great mistake. He tells her she was right, adding, “I have lived too long in foreign parts.” Nevertheless, he goes back to his former life in Geneva.

The scene in the Coliseum, where Winterbourne comes upon Daisy and Giovanelli, reveals Winterbourne at his most pathetic. Nowhere does he respond with less thought or reflection. He immediately takes the fact of Daisy’s presence there, at that hour and in that situation, as evidence of her worthlessness. Still, Winterbourne’s reaction is complex. He is horrified but also relieved, and he is “angry with himself” for having wasted so much time bothering about “the right way of regarding Miss Daisy Miller.” In a way, Winterbourne feels let off the hook, but whether he feared that Daisy was innocent or guilty remains unclear. At Daisy’s funeral, Giovanelli tells Winterbourne that Daisy was beautiful and also innocent, which serves as a disturbing revelation for Winterbourne. After all, if anyone should know the extent of Daisy’s culpability, it is Giovanelli, her “accomplice” in all her presumed wrongdoing. Giovanelli’s comment, which he tosses out as an afterthought, suggests that Winterbourne judged Daisy wrongly, and it strongly affects Winterbourne.

The scene at the Coliseum is rife with thematic and symbolic content. The ancient arena is where generations of Christian martyrs were sent to do hopeless battle with lions and other wild beasts. Daisy is not necessarily a martyr to anything, but in a way she is indeed trying to take on the threatening forces of Roman high society. For Winterbourne, the Coliseum is associated with his beloved poet Byron. Winterbourne thinks of a particular passage in a long verse-drama of Byron’s called “Manfred” when he becomes aware of the presence of Daisy and Giovanelli. However, Winterbourne’s understanding of Byron is at best superficial, and his thinking of a Romantic poet just here, on the verge of writing Daisy off, is ironic, given what the Romantic poets actually stood for: rebellion and unconventionality.

When Mrs. Costello asks Winterbourne if he thought Daisy might love him back if he indeed loved her, she, for the first time since the outing at Chillon, raises the possibility that Winterbourne might have entertained romantic feelings for Daisy. Not surprisingly, Winterbourne sidesteps the issue, replying only that Daisy meant “she would have appreciated one’s esteem.” Winterbourne is saying that for all her much-vaunted lack of concern with what people thought of her, Daisy cared what he thought. However, Winterbourne uses the impersonal pronoun one’s not my both to distance himself from the whole matter and as if to suggest that Daisy’s message expressed something about her relationship with the whole community in Rome. Had Winterbourne embraced the possibility that Daisy’s affections and hopes were for him alone, his guilt over judging and dismissing her would necessarily increase.

When Winterbourne tells Mrs. Costello that she was right about his making a mistake with Daisy, he acknowledges her foresight and accepts that his mistake was great. In other words, his actions and inactions had meaning for him, and choosing differently might have altered or affected his life. Had he not suspected Daisy of immorality, or had he not denied his feelings for her, he may have found a measure of happiness that is now out of reach. The conclusion of the novel is poignant. James not only suggests that Winterbourne went right back to his former life, but he states this in a way that suggests that the whole story has just been part of an ongoing process of inconsequential gossip, with no importance for anyone—us, the people involved, or the man or woman telling the story. Although Winterbourne is clearly affected by what happened with Daisy, the fact that he can so smoothly return to his normal life suggests that he is, disturbingly, dismissing Daisy and her humanity.