In a suburban American town during the late 1950s, two young neighbors, Juli Baker and Bryce Loski, meet in second grade. Juli instantly knows Bryce is the one for her, while Bryce is less certain and tries to avoid her persistent advances. Through middle school, Juli continues to see the best in Bryce, admiring him from afar despite his indifference. As the years progress, Bryce becomes increasingly wary of Juli's fervent interest and grows annoyed by her seemingly odd habits, like her dedication to raising chickens and her passion for a large sycamore tree. Meanwhile, Juli's feelings for Bryce remain strong, convinced he has a deeper, more caring side underneath his aloof exterior.

As they enter junior high, Juli begins to see flaws in Bryce's character that she previously overlooked. Bryce's attempts to fit in with his friends and his treatment of her begin to hurt Juli. Concurrently, Bryce starts to see Juli in a new light, appreciating her unique qualities and her strong sense of self. The gap between their perceptions widens as Juli grapples with her changing feelings for Bryce. As they both face various personal and family challenges, they begin to reassess what they value in themselves and each other, leading to an eventual pivotal moment that forces them to confront their true feelings and reconsider the dynamics of their relationship.