When Mr. Henry Dashwood dies, leaving all his money to his first wife's son John Dashwood, his second wife and her three daughters are left with no permanent home and very little income. Mrs. Dashwood and her daughters (Elinor, Marianne, and Margaret) are invited to stay with their distant relations, the Middletons, at Barton Park. Elinor is sad to leave their home at Norland because she has become closely attached to Edward Ferrars, the brother-in-law of her half-brother John. However, once at Barton Park, Elinor and Marianne discover many new acquaintances, including the retired officer and bachelor Colonel Brandon, and the gallant and impetuous John Willoughby, who rescues Marianne after she twists her ankle running down the hills of Barton in the rain. Willoughby openly and unabashedly courts Marianne, and together the two flaunt their attachment to one another, until Willoughby suddenly announces that he must depart for London on business, leaving Marianne lovesick and miserable. Meanwhile, Anne and Lucy Steele, two recently discovered relations of Lady Middleton's mother, Mrs. Jennings, arrive at Barton Park as guests of the Middletons. Lucy ingratiates herself to Elinor and informs her that she (Lucy) has been secretly engaged to Mr. Ferrars for a whole year. Elinor initially assumes that Lucy is referring to Edward's younger brother, Robert, but is shocked and pained to learn that Lucy is actually referring to her own beloved Edward.
In Volume II of the novel, Elinor and Marianne travel to London with Mrs. Jennings. Colonel Brandon informs Elinor that everyone in London is talking of an engagement between Willoughby and Marianne, though Marianne has not told her family of any such attachment. Marianne is anxious to be reunited with her beloved Willoughby, but when she sees him at a party in town, he cruelly rebuffs her and then sends her a letter denying that he ever had feelings for her. Colonel Brandon tells Elinor of Willoughby's history of callousness and debauchery, and Mrs. Jennings confirms that Willoughby, having squandered his fortune, has become engaged to the wealthy heiress Miss Grey.
In Volume III, Lucy's older sister inadvertently reveals the news of Lucy's secret engagement to Edward Ferrars. Edward's mother is outraged at the information and disinherits him, promising his fortune to Robert instead. Meanwhile, the Dashwood sisters visit family friends at Cleveland on their way home from London. At Cleveland, Marianne develops a severe cold while taking long walks in the rain, and she falls deathly ill. Upon hearing of her illness, Willoughby comes to visit, attempting to explain his misconduct and seek forgiveness. Elinor pities him and ultimately shares his story with Marianne, who finally realizes that she behaved imprudently with Willoughby and could never have been happy with him anyway. Mrs. Dashwood and Colonel Brandon arrive at Cleveland and are relieved to learn that Marianne has begun to recover.
When the Dashwoods return to Barton, they learn from their manservant that Lucy Steele and Mr. Ferrars are engaged. They assume that he means Edward Ferrars, and are thus unsurprised, but Edward himself soon arrives and corrects their misconception: it was Robert, not himself, whom the money-grubbing Lucy ultimately decided to marry. Thus,x Edward is finally free to propose to his beloved Elinor, and not long after, Marianne and Colonel Brandon become engaged as well. The couples live together at Delaford and remain in close touch with their mother and younger sister at Barton Cottage.