Zoe Sarah Bolger is a 15-year-old girl who is taken to the doctor for back pain and learns she has scoliosis, which will require wearing a back brace for several years until she stops growing. She fears being marginalized at school and resents her mother for insisting on the brace, while her father grapples with the idea that the condition is inherited from him.
Noticing a slightly older girl named Shelby Emily Osment in the neighborhood, Zoe reaches out to offer friendship. Zoe begins babysitting for a married couple, Chance John Corbett and Vera Jenna Fischer, and Chance, a photographer, suggests that Zoe could become a model. Having developed a crush on Chance, Zoe impulsively kisses him one evening as he drops her off at home.
Shelby opens up about her own home life, explaining to Zoe that her father is an alcoholic who is abusive toward her and her mother, and that Shelby's conservative, controlling parents keep her at home when she isn't working. As the school year progresses, the two girls grow closer, sharing fears and dreams, and Zoe’s eyes are opened to Shelby’s harsh realities behind the neighborhood’s ordinary surface.
One day after school, when Shelby isn’t there to walk home with her, Zoe goes to Shelby’s house and sees police cars out front. Later, she learns that Shelby called them out of frustration over her father’s violence, a moment that marks how their bond is tested by danger and truth.
Zoe is then unhappy to learn that she was awarded a summer job for the park district, partially because she is considered handicapped. Accepting the new job causes her to stop babysitting during the week. Chance suggests she do a photo shoot that weekend, during which the two end up flirting and several provocative shots are taken, intensifying the pull between them.
Despite the emotional and physical hardships Zoe and Shelby experience, their friendship deepens and evolves, leading to significant changes in both of the girls’ lives. However, their relationship is challenged when Shelby’s mother catches the girls kissing. Shelby’s mother becomes upset and forbids her from seeing Zoe, adding a barrier that tests their loyalty and courage.
Meanwhile, Vera becomes suspicious that something happened between Zoe and Chance on the weekend; she confronts Zoe at her park job to tell Zoe that she’s no longer needed as a babysitter. The trust between the adults around them frays as secrets and misunderstandings start to shape the girls’ futures.
After three years, Zoe stops needing her back brace, Shelby gets married, and Zoe attends as a guest. Later on, Chance visits Zoe at her work and invites her over to his place while Vera and their children are away on a trip with Vera’s parents. However, when Chance takes his clothes off, wanting to have sex during her visit, Zoe realizes that she doesn’t want to go through with it, choosing her own boundaries and future.
In the concluding scene, Shelby briefly visits Zoe before Zoe departs for college, as Zoe’s mother lets Shelby know that Zoe will be leaving. Wishing Zoe luck, both girls promise to keep a bit of each other in their hearts, underscoring a lasting, nuanced friendship formed against all odds.
