The heroine Fanny Price lives with Sir Thomas and Lady Bertram, her wealthy Aunt and Uncle, and her cousins at their estate, at Mansfield Park. Fanny is a pious evangelical and is in love with Edmund, her cousin. Sir Thomas leaves for a year on a business trip. Henry and Mary Crawford visit. Mary and Edmund become close to each other and Henry starts flirting with Maria, making her treat her rich fiancé, Mr. Rushworth, badly. The Crawfords and young Bertrams decide to stage a slightly risqué romantic play and begin rehearsals. Fanny disapproves. Edmund is reluctant to join in but is persuaded by Mary. Sir Thomas returns and forbids them to produce the play. Maria marries Mr. Rushworth, and the Crawfords leave.
Henry Crawford returns to Mansfield Park, and falls in love with and proposes to Fanny. Fanny refuses him. Fanny is sent home to her own family in Portsmouth to see how depressing poverty can be in the hopes that will make her marry Henry, who is rich. Henry has an adulterous affair with Maria, causing a major scandal and Julia, another cousin elopes with Mr. Yates. Fanny returns to Mansfield Park and helps care for the eldest son Tom whose dissolute behavior has injured his health. Edmund realizes that Mary is immoral, telling her:
"Your keen adaptability to my brother's possible demise sends a chill through my heart. A chill. Happily planning parties with his money. You shush my father like a dog at your table, and then you attack Fanny for following her own, infallible guide concerning matters of the heart. All of this leads me to believe that the person I've been so apt to dwell on for many months has been a figure of my own imagination, not you, Miss Crawford. I do not know you, and I'm sorry to say, I have no wish to."
He then returns to Mansfield Park and marries Fanny.