Jessica secretly listens to the radio after school lessons one day, and becomes confused over lyrics that describe love ("Hold me, hold me, never let me go, until you've told me...") Her mother, Sister Jacobs, is one of her father's three wives, and tells Jessica that she is happy as she is very close to her 'sister' wives. Soon after, Jessica is getting ready to welcome home the son of the brethren leader of the community, the nineteen-year-old Isaac King who has been fighting in the Korean War.
Jessica is upset that her father will not buy her any girls shoes and instead wears boys' shoes with the socks rolled down. Jessica welcomes Isaac, but is reprimanded after asking what Korea is like, as she has never left Short Creek. Isaac and Jessica show an attraction towards each other and happily dance outside with the rest of the community. Meanwhile, President King calls a meeting with the Brethren where he claims God has told him he must take another wife. Jay Jacobs is disturbed to find that President King is referring to his carefree daughter, Jessica, but puts aside his worries as it is 'God's will'.
In church the next day Isaac shows up late and stares at Jessica through the service. As the community file out of the church President King tells Jessica that she ought to start thinking about marriage. Jessica shows slight shock and soon catches Naomi kissing a teenage boy behind a shed. She shares her worry that she will be married off to an old man, and Naomi claims she is going to escape to Las Vegas to become an actress. On a trip to pick plums, Isaac shows great discomfort and anger when teenagers in a passing car ask him if Jessica and Naomi are his wives and call him a "plig" (short for Polygamist). It soon becomes apparent that Isaac has feelings for Jessica as after she gives him one of her clay animals, he claims that he'll keep it next to his heart. Jessica's mother uneasily orders her daughter not to talk to Isaac so much as '...it don't look right." Jessica stops talking to Isaac so much, though he does tell her about flying in an airplane when she asks him to describe it. When Jessica refuses to talk to him, Isaac states that "So they're afraid we might like each other. They're going to marry you off soon, Jessie." On a trip, while bathing their feet in a lake, Jessica and Naomi discover that Isaac's younger sisters have drowned, despite Isaac diving in to recue them. At their funeral, Isaac loses his temper with Jessica and claims that Short Creek isn't connected to the outside world. Jessica retorts that she wants to be good and live by the way of God.
Naomi then attempts to leave Short Creek. After walking for a while she naively accepts a ride off two men and tries beer for the first time. The two men attempt to rape her, but are stopped by President King who was following Naomi, having been aware of her wild nature for a while. Naomi, crying is driven back to Short Creek.
President King then tells Jessica of his intentions to marry her, at which Jessica bursts into tears. After much persuasion she agrees, as she knows she has no choice in the matter. Isaac then turns up at her house drunk late one night. She comes outside in her nightgown, disgusted by his drunkness. When she tries to run away, he grabs hold of her, which scares her, and then he tells her that he wants to run away. Jessica runs away stating "I'm Jessica Rae Jacobs, and I'm proud of it!"
Isaac finds out from his mother the next morning that his father has decided to marry Jessica. He's furious, not only because of his feelings for her, but because of her youth and the fact that his mother will be neglected once again. He angrily confronts his father and tells him that he doesn't want the Kingdom of Heaven or any of it. His father disowns him. One morning after tearfully trying on an old wedding dress, Jessica discovers that Naomi has been secretly married off to an old man to tie her down. After finding this out, she runs to Isaac and confesses her love for him. The two kiss and make plans to leave at the pioneer celebrations the next afternoon. Jessica secretly packs her belongings and the two escape in Isaac's car. In a restaurant, Jessica realizes how much she stands out from the crowd. Isaac promises her that he'll buy her some girls' shoes with straps and they'll stay in a motel where "magic fingers" (massaging mattresses) will put her to sleep. He also claims that he will sleep on the floor until they're married. Just as their bus arrives, they notice many police cars going towards Short Creek and realize it must be a raid. Jessie refuses to board the bus and drives back to Short Creek to warn everyone, leaving a tearful Isaac behind.
The community peacefully co-operate, leaving the authorities to feel guilty as they split the many families up, including a pregnant Naomi. Jessica sadly boards a school bus with her mother and siblings, ready to be taken off to an army barracks to be re-educated.
Two years later, we see the women at the barracks getting ready to board the buses to go back to Short Creek. Jessica, now wearing clothes more suited to a girl her age is wearing Isaac's dogtags around her neck. As she looks around, she sees Isaac standing outside a little blue car. Her mother tells Jessica to "Run, while you still have a chance" and Jessica hugs her mother goodbye, promising to write. Jessica shyly approaches Isaac, who hands her her box of clay animals which he has kept for two years. They happily embrace and drive away together.