In the year 1970, Margaret Simon, an eleven-year-old girl, faces a tough transition as her family relocates from the vibrant streets of New York City to a quiet suburb in New Jersey due to her father, Herb, receiving a promotion. This news leaves Margaret feeling upset, as she dreads leaving behind her friends and, most importantly, her cherished paternal grandmother, Sylvia. In her quest for companionship and understanding, Margaret begins to converse with God, sharing her worries and aspirations.
Upon her arrival in New Jersey, Margaret quickly forms a friendship with her neighbor, Nancy Wheeler. Nancy introduces her to a group of girls, including Gretchen Potter and Janie Loomis. At school, Mr. Benedict, their teacher, sets a semester-long research project in motion. During this assignment, Margaret confides in Mr. Benedict about her complex feelings regarding religion. With a Christian mother and a Jewish father, she explains how her family has left the decision of her religious path entirely up to her, which only adds to her inner turmoil.
As Margaret delves deeper into her identity, she learns about her family dynamics, particularly the estrangement between her mother, Barbara, and her devoutly Christian parents, Paul and Mary. This revelation unfolds as she visits New York City with her grandmother, where she takes the step of asking Sylvia to accompany her to temple, an experience that Sylvia happily embraces. Meanwhile, Barbara becomes increasingly involved with the PTA, navigating through her parental duties, which sadly takes her away from her passion for art.
Alongside her friends, Margaret anticipates the strange yet exciting milestones of puberty. From wearing a bra to experiencing first kisses, they navigate this transformative stage together. One memorable moment occurs at a birthday party, where she shares her first kiss with Philip Leroy, a boy who piques her interest during a game of spin the bottle. The excitement grows again when the class views a film about menstruation, propelling Margaret and her friends into a frenzy over the onset of their periods. As her friends begin to experience these milestones ahead of her, including Gretchen and Nancy, Margaret's impatience leads her and Janie to purchase sanitary products at a local pharmacy for when her time finally arrives.
A pivotal moment occurs during a trip to New York City with Nancy, where Margaret uncovers Nancy's deception about her own menstrual experience. Later, in school, Margaret partners with Laura Danker, a girl ostracized by her classmates for being taller and seemingly more mature. However, during their time in the library, misunderstandings arise when Margaret unwittingly brings up rumors about Laura, leading to a confrontation that leaves both girls feeling unsettled.
As spring break approaches, Margaret dreams of visiting Sylvia in Florida. Yet this plan is derailed when Paul and Mary reach out, expressing a desire to meet Margaret for the first time, leading to an unexpected visit that stirs tension within the family. The situation escalates during an awkward dinner, where Paul and Mary suggest that Margaret might benefit from Sunday school, igniting a fierce rebuttal from Sylvia, who insists that Margaret has already chosen Judaism by attending temple. The resulting argument forces Margaret to confront her feelings very directly, as she vehemently claims indifference toward religion and doubts God's existence.
Returning to school, Margaret submits her research paper, reflecting her frustrations with religion, and takes steps to mend her relationships with her parents and Sylvia. As the school year concludes, she thanks Mr. Benedict for his supportive guidance. In an encouraging twist, she befriends Laura, inviting her to join in dances, stepping beyond the initial friction between them. Barbara, shifting her priorities, informs Nancy’s mother that she will no longer partake in PTA tasks, allowing her more time for her art.
Just before embarking on a summer camp adventure, Margaret shares a sweet exchange with Nancy's older brother, delivering hope for their budding connection upon her return. Finally, back at home, she discovers that her first period has arrived, rejoicing in this newfound milestone. Following this revelation, Margaret resumes her conversations with God, sealing her journey of self-discovery and acceptance.
