Isabel Archer's aunt comes to America after the death of Isabel's father in order to take her niece to Europe. On her arrival in England, Isabel meets her cousin Ralph, her uncle, Mr. Touchett, and the great nobleman of the area, Lord Warburton, who immediately falls in love with her. After a short time, Warburton proposes to Isabel, but she turns him down, maintaining that she cherishes her freedom and independence too much to marry. A short time later, her journalist friend Henrietta Stackpole arrives in England and tells Isabel that her American suitor Caspar Goodwood has followed Isabel to England.
During a visit to London, Isabel encounters Caspar Goodwood, who tries to convince her that she should marry him. Again, Isabel says that she must have time to see the world and make a few independent judgments. She promises Goodwood that she will discuss the subject again in two years. He leaves, promising to remain in America for this time.
While in London, Isabel hears of the sickness of her uncle. She returns to his home, Gardencourt, where she finds him dying. She also finds another guest, Madame Merle, an old friend of Mrs. Touchett's. During the long days when the house is involved with sickness, Isabel and Madame Merle become good friends.
Ralph Touchett knows that his father plans to leave him a huge fortune, but he also knows that he is slowly dying himself and does not need much money. He therefore convinces his father to leave some of his fortune to Isabel.
After Mr. Touchett's death, Isabel becomes a great heiress. She continues to travel with her aunt and they go to Mrs. Touchett's home in Florence, Italy. Here, Madame Merle introduces Isabel to her old friend Gilbert Osmond. Madame Merle has already instructed Osmond to be nice to Isabel because she thinks that Gilbert should marry her.
After some time, Isabel believes that she is in love with Osmond. She maintains her independence by refusing to listen to any advice. Everyone is opposed to her marrying Osmond because all feel that he is a worthless fortune hunter.
Some years later, Isabel knows that she has made a mistake. Gilbert Osmond, now her husband, has tried to break Isabel's independent nature and has tried to make her obey his every wish. He wants Isabel to be as quiet and obedient as is his daughter. Pansy, the daughter, has been brought up in a convent and has been taught to obey her father in everything. Thus when the father disapproves of the young man that Pansy is in love with, she must submit to his wishes.
When Isabel receives a letter telling her that her cousin Ralph is dying, she wants to go to England to visit him. Osmond opposes the trip because it would not look proper. At this time, Isabel discovers that Pansy is actually the illegitimate child of Madame Merle and Gilbert Osmond. She then realizes that her friend Madame Merle tricked her into an imprudent marriage with Osmond, and with this knowledge Isabel leaves for England in spite of her husband's disapproval.
In England, she confesses the mistake she made in marrying Osmond, and Caspar Goodwood pleads with her to leave her husband. Isabel, however, feels that she cannot forsake the sacred bonds of marriage and feels that Pansy needs her help. She therefore decides to return to Osmond in spite of her dislike for him.