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.