The Summer I Turned Pretty follows the life of Isabel "Belly" Conklin, a teenage girl who has spent every summer at Cousins Beach with her family and friends. This year, she finds herself navigating the complexities of adolescence and her feelings towards two brothers, Conrad and Jeremiah Fisher, who have been her lifelong summer companions. As Belly matures, she becomes more aware of her emotions and desires, which creates tension and rivalry within the relationships she holds dear.
The story explores themes of love, heartbreak, and the transition from childhood to adulthood. Belly's experiences during that summer challenge her understanding of friendship and family dynamics. The rivalry between the brothers intensifies as they each pursue their feelings for her, leading to a whirlwind of romantic confusion and self-discovery for Belly.