An American who has lived most of his life in Europe, Winterbourne is the type of Europeanized expatriate that Mrs. Costello and Mrs. Walker also represent. He is also closely associated with New England Puritanism: he makes his home in Geneva, “the dark old city at the other end of the lake” that James is at pains to identify as the wellspring of Calvinism, not out of necessity but by choice. In many ways, Winterbourne is as central a character as Daisy and may very well be the story’s true protagonist. Certainly, he is the novel’s central consciousness, the character through whose eyes we see and experience everything.
Early on, we are told that Winterbourne is “addicted to observing and analyzing” feminine beauty. However, he does not appear to be a very deep or discriminating thinker. He spends time with his aunt not because of affection or because he takes pleasure in her company, but because he has been taught that “one must always be attentive to one’s aunt.” Winterbourne seems to hold in high regard what Mrs. Costello tells him, about the Millers as much as anything else. Out loud he defends Daisy, albeit rather feebly, but the whole novel is, in a sense, the story of Winterbourne’s attempts and inability to define Daisy in clear moral terms. Winterbourne is preoccupied with analyzing Daisy’s character. He wants to be able to define and categorize her, pin her down to some known class of woman that he understands. Daisy is a novelty to him. Her candor and spontaneity charm him, but he is also mystified by her lack of concern for the social niceties and the rules of propriety that have been laid down by centuries of European civilization and adopted by the American community in Rome. He befriends Daisy and tries to save her but ultimately decides that she is morally beyond redemption.