Iris [Kara Hayward] Deerborne is a teenager living in a rural Oklahoma town in 1960. The shy Iris is emotionally abused by her mother Francie Deerborne [Jordana Spiro], who wishes her daughter were more glamorous. At home, her father Hank Deerborne [Shea Whigham] tries to shield his family from the town's judgment. At school she is bullied by many of the other kids, especially the popular but insecure “queen bee” Clarissa Dell. Iris harbors a quiet attraction to Jeff Owings [Lucas Jade Zumann], a fellow student who works for her father. Iris frequently sneaks out at night to swim in a local pond, wishing that she could disappear.
One day, as she walks to school, Iris is accosted by several boys. Maggie Richmond [Liana Liberato], a new girl in town, chases them off and tells everyone her father is a glamorous photographer for Life magazine who has photographed movie stars and dignitaries. Later, she confesses that her father actually works for an agricultural trade publication. Maggie's family includes her mother Grace Richmond [Malin Åkerman], and Maggie quickly befriends Iris, inviting her into a circle that’s eager to stand out from the town’s narrow conventions.
Iris and Maggie become fast friends, and Maggie convinces Iris to skip school so they can get makeovers, with hairdos from the local stylist Hazel Atkins [Adelaide Clemens]. Iris’s fresh look and new confidence begin to win her greater acceptance among the other girls, who are keen to snag dates for the upcoming school dance. At the dance, Iris finally finds the nerve to dance with Jeff Owings [Lucas Jade Zumann], much to the surprise of their peers.
Maggie’s family is thrilled when she’s asked to the prom by a popular football player, Craig Butler. Maggie’s mother takes her dress shopping for the occasion, and Maggie again visits Hazel Atkins for a new hairdo. Maggie learns that the photograph everyone believes to be Hazel’s dead husband is actually her brother. After sharing a tender moment, Hazel touches Maggie’s cheek, and Maggie warms to the moment, then suddenly flees.
That night, Maggie goes to the pond with her new circle of friends and, frustrated by the social fallout around her, ends up having sex with Craig Butler by the water. Afterwards, a distraught Maggie goes to Iris, and the two share a drunken kiss before Maggie rushes away, leaving Iris unsettled by what she’s witnessed.
The next day, Iris learns that Craig has given Maggie a promise ring. Maggie invites the other girls and their dates to the pond to skinny-dip, an act Iris regards as a betrayal of the special place she had shared with Maggie. The confrontation that follows erupts into a feud in which Iris accuses Maggie of lying to everyone, while Maggie retorts with the nickname the other kids used for Iris’s insecurities. Ashamed of what she’s done and the people she’s with, Maggie runs to Hazel’s house, and the two kiss before Maggie enters.
Late that night, a neighbor’s sighting confirms the town’s gossip: Hazel and Maggie’s relationship has become the talk of the town. A group of men vandalize Hazel’s car and threaten her, prompting Hazel to leave town. Maggie’s father beats her again, then breaks down in tears over his idealized image of his daughter. Maggie apologizes to her parents, tells them that they won’t have to worry about her anymore, and flees into the night.
The next morning, Iris learns about what happened. She finds Maggie’s father Gerald Richmond and the police by the pond, a site locally known as the place where Jeff’s mother is believed to have committed suicide. Gerald Richmond asks Iris to tell Maggie to come home and says he doesn’t care about Maggie being “bad” anymore. Iris stands up for Maggie and tells him that she was never “bad.” The police are unable to find Maggie, either alive or dead. When a group of boys harass Iris on the road again, she throws stones at them just as Maggie did. Overhearing her mother gossip with a friend, Iris insists that Maggie isn’t dead but has fled far beyond the town’s narrow-minded reach. She then tells her mother that she’s going on her first date with a boy. Iris and Jeff kiss by the pond and then go swimming.
