Isabel Archer, an independent and curious young woman from Albany, New York, arrives to the English countryside at the invitation of her maternal aunt Mrs. Touchett. Having never met their American relative, Isabel’s uncle Mr. Touchett and her cousin Ralph greet her warmly at Gardencourt (the Touchett family estate). They are both immediately taken by Isabel’s beauty and good nature after she appears like an apparition in their doorway. Mr. Touchett and Ralph are both unwell due to old age and consumption, respectively. Also present at this first introduction is the dashing Lord Warburton, the Touchett’s neighbor, who is similarly enchanted upon meeting Isabel.
Spending four months at Gardencourt, Isabel is grateful for the Touchett’s goodwill and charmed by their reclusive, yet beautiful, rural lifestyle. She spends time daily with her uncle and cousin, her fresh perspective and energy bringing them great joy despite their ill health. Isabel’s aunt continues to favor her but spends most time isolated from the family in her rooms, as is her custom; Mr. and Mrs. Touchett have succeeded in a long marriage by spending the majority of their time apart, often living in different countries.
During her stay at Gardencourt, Isabel also spends time with Lord Warburton, who offers her a tour to inspect the architecture and grounds at Lockleigh, his neighboring castle property. He also introduces her to his two sisters. When Warburton proposes suddenly, Isabel is shocked. She rejects his offer as politely as she can, and is relieved by his good character in his continued visits to the Gardencourt in as friendly and gentlemanly a manner as ever.
Gardencourt is also transformed by the arrival of Henrietta Stackpole, an American journalist whom Isabel idolizes for her successful career and personal independence. Henrietta is reporting on European lifestyles for her newspaper column. Ralph accompanies Isabel and Henrietta to London to experience the capital’s social scene. Despite Isabel’s admiration for her friend, Henrietta’s frank and even tactless personality ruffles a few feathers amongst the English elite.
While in London, Isabel rejects yet another request for her hand in marriage. The wealthy and charismatic American businessman Caspar Goodwood has followed her to England to pursue their burgeoning relationship. As with Warburton, Isabel is attracted to Goodwood—perhaps even more strongly—but cannot see herself marrying him. She is concerned that marriage to either man will result in the sacrifice of her personal freedoms. Isabel’s current desire is to experience exotic adventures throughout Europe without being tied to down to anyone else’s influence. As with Warburton, she expresses to Goodwood her desire for total independence and explains that she would not make a good wife.
Madame Merle, an American ex-patriate and old friend of Mrs. Touchett’s, visits Gardencourt and strikes up a firm friendship with Isabel. During this time, Mr. Touchett’s health declines further. Ralph, who is fascinated by his cousin and wishes to fulfil her desire for a life of personal freedom, convinces his father to leave a significant portion of his will to Isabel. Upon Mr. Touchett’s passing, Isabel is grief-stricken and also overwhelmed by the enormity of her surprising new financial assets. She comes to accept her uncle’s generous gift, vowing to use her money to make meaningful change in the world. Despite Ralph’s designs for new wealth to guarantee Isabel’s independence, Henrietta and Mrs. Touchett warn Isabel of the responsibilities and risks of financial prosperity.
Isabel begins traveling Europe, visiting various locations in England, France, and Italy. In Florence, Madame Merle introduces Isabel to another American expatriate named Gilbert Osmond. Osmond is an older gentleman who fascinates Isabel due to his worldly experiences, artistic taste, and non-conforming personal life. The two spend time together, with Isabel unaware that Osmond and Madame Merle are collaborating for Osmond to take advantage of Isabel and her new wealth. After four months Osmond proposes to Isabel. Despite her family and friends’ mistrust of Osmond, Isabel accepts his proposal of marriage, believing that their union will lead to her financing his artistic exploits as a worthy cause. Usually a perceptive individual, she is completely blind to his serious flaws in character.
Skipping forward two years in time, Isabel and Osmond are living in Rome in an unhappy marriage. Osmond treats Isabel as a mere addition to his art collection, and Isabel is unhappy with the lack of a true partnership. She has discovered that Osmond is a deceitful, selfish, and dominating individual. However, Isabel has come to adore Osmond’s daughter, Pansy, an intelligent yet meek girl who obeys her father’s every wish. Isabel’s acquaintance from childhood, Edward Rosier, is a young art collector who falls in love with Pansy. Isabel approves wholeheartedly of the love match but Osmond opposes Rosier’s courtship on the grounds that the young art collector has little wealth and career prospects. Osmond prefers Pansy to marry Lord Warburton instead, for the English aristocrat has shown interest is the young woman. Isabel is concerned that Warburton is only pursuing Pansy to be close to Isabel, as he may still be in love with her.
Isabel learns that Ralph’s health has seriously declined, and he is nearing death. She desperately wants to visit Gardencourt to be with him, but Osmond forbids it. Furthermore, Isabel learns that Pansy is the child of an affair between Osmond and Madame Merle, a secret that has been hidden throughout Pansy’s life. Isabel comes to pity her previous friend, Merle, for her immoral and lonely existence. Before departing for England, Pansy begs Isabel to return to Rome, as the girl adores her stepmother. Isabel leaves without Osmond’s permission.
At Gardencourt, Isabel reconnects with Ralph and comforts him until he passes. She is devastated by his loss. Goodwood visits her at Gardencourt, where he reiterates his commitment to her and passionately suggests that they run away together. Upon looking for her the next day, he discovers she has left the estate. Henrietta suggests that Isabel has returned to her husband in England.