Tammy, a seventeen-year-old tomboy who lives near a Louisiana swamp with her grandfather, lay preacher John Dinwitty, complains to her best friend, a goat named Nan, about their sheltered existence. When Grandpa announces that he is going to investigate the site of a plane crash, a bored Tammy insists on accompanying him, and they soon discover the pilot, Natchez landowner Peter Brent, floating unconscious on the river. They bring Peter home, where Tammy nurses him and prays for his life. When Peter finally recovers five days later, Tammy credits God and onion poultices, and instantly charms Peter with her straightforward, folksy approach to life. He recuperates for another five days, during which Tammy falls in love with him. Peter, however, has a girl friend, socialite Barbara Crain, and as soon as he discerns Tammy’s feelings, he prepares to leave, promising never to forget her. Weeks later, when Grandpa is jailed for bootlegging corn liquor in an attempt to make enough money to send Tammy to school, he insists that she move in with Peter’s family. Tammy and Nan walk all the way to Peter’s home, where his friends are practicing dances for the upcoming Pilgrimage Week under the watchful eye of his mother, who views the festival as an opportunity to show off their estate. An exhausted Tammy falls asleep on the porch, and when Peter discovers her, he assumes that Grandpa has died. In the morning, after Tammy sees herself in a mirror for the first time, Peter brings her breakfast, and then explains that he is farming experimental tomatoes in the hopes of reviving the failing farm. He kisses her on the cheek, an innocent gesture that makes her swoon with pleasure. Downstairs, she discovers indoor plumbing and meets Peter’s father, Professor Brent, and Aunt Renie, who dabbles in painting. At breakfast, Mrs. Brent, a leader in the temperance league, is horrified to learn that Grandpa is not dead but incarcerated, and although an embarrassed Tammy announces she will leave at once, Peter apologizes and urges her to stay, and Renie concurs. Later, Peter muses over Barbara’s preference for city life, and is pleased by Tammy’s enthusiasm for living off the land, wishing that everyone could share her desire for nothing more than food, shelter, family and love. When he hugs her, she puckers her lips, but he merely kisses her forehead. A month passes, during which Mrs. Brent, preparing feverishly for Pilgrimage Week, criticizes Tammy for her unrefined speech, and Renie complains that she has wasted her life by failing to live as a Bohemian in Paris. One day, Peter’s rakish friend Ernie invites Tammy on a date. Peter follows them and interrupts Ernie’s attempts to seduce the naïve girl. After a brief squabble with Ernie, Peter pulls Tammy into his car, where he inadvertently delights her with his demonstration of how a “wolf” behaves. They share a night in town, after which she asserts that everyone in his family is afraid—Renie of doing what she loves, Mrs. Brent of dying, Prof. Brent of facing the world, and Peter of being a failure. A disturbed Peter agrees that he has been drifting since the war, then lightheartedly asks her to help him find himself. One day soon after, Barbara arrives with her uncle, wealthy advertising executive Alfred Bissle, who scorns Peter’s inclination to revive the farm rather than work at the ad agency. After Tammy defends land ownership as the only true wealth, a jealous Barbara humiliates her, and Tammy spends the evening in the barn with Nan. Peter later assures her that he has not taken the job, and when Tammy sympathizes with his desire to please his mother and girl friend, Peter marvels at her wisdom, but continues to view her as a child. As Pilgrimage Week begins, Tammy encourages Al to eat a hearty breakfast, and he is thrilled to discover that his constant indigestion has been alleviated. Downstairs, Renie secretly outfits Tammy in her Grandmother Cratchett’s antebellum gown, instantly transforming her into a lovely woman. Everyone is struck silent by her beauty, especially Peter, but Mrs. Brent breaks the spell by rhapsodizing over Barbara’s dress. Mrs. Brent then asks Tammy to play the part of Grandmother Cratchett for the evening, hoping this will excuse her rough rural speech, and Tammy takes to the charade with gusto, spinning a charming tale of the pioneer Brents that soon draws all of the guests around her. Peter prompts her to recount how she met Grandfather Brent, and stands close to her as she narrates the romantic story. After Barbara quickly interrupts, Ernie asks Tammy out again, this time respectfully, but she rejects him. Late that night, a violent storm rages, and although Tammy runs out to the garden to help Peter cover the tomatoes, they are destroyed, and an inconsolable Peter decides to accepts Al’s job offer. At breakfast, Renie announces that Tammy has inspired her to move to New Orleans to paint, and that she plans to sell the house, while Al declares that seeing Tammy revive the charm of the Old South has made him value the estate. The professor, grasping the hands of his delighted wife, adds that he has learned not to be afraid of life. Just then, Osia, the housekeeper, reveals that Tammy has gone, and Renie warns Peter that he should not go after her unless he loves her. Without speaking, he rushes out the front door, where Barbara has just arrived bearing a newspaper which exposes Tammy’s grandfather’s bootlegging charge. After Barbara gloats that Mrs. Brent will be furious, Peter tells her that their love, which does not allow for compromises, is not strong enough. Hours later, Peter finds Tammy by the river near her houseboat. He has secured Grandpa’s release from jail, but before Tammy can greet her grandfather, she pauses to receive her first real kiss.