Melissa, María Valverde, is a shy 15-year-old who lives with her mother Daria and her heavy-smoking grandmother, Geraldine Chaplin. Her father works overseas on an oil rig, leaving the family to navigate a summer that will test her boundaries and feelings. She shares a close bond with her grandmother, but senses a growing distance from her mother as days unfold with new, uncomfortable awakenings.
During a summer pool party at the home of the wealthy classmate Daniele, Primo Reggiani takes Melissa to a secluded spot, where she finds herself drawn into a moment of sexual intimacy that leaves her both numb and more hungry for attention. Although the encounter isn’t romantic, Melissa’s feelings for him deepen, shaping a complicated view of love, power, and desire.
After a failed attempt to capture his interest, Melissa heads to a bar where Daniele is with his friends. He invites her back to his place, and she loses her virginity to him. She tells him she loves him, but his cold rejection cuts deep. Humiliated, Melissa vows to protect herself from getting hurt again, choosing to focus on her own satisfaction and needs.
Around the same time, Melissa’s parents decide to move Elvira, her heart-weak grandmother, to a nursing home. The plan strains Melissa’s relationship with her mother, Daria, who struggles to notice the emotional storms brewing beneath her daughter’s outward calm. When Elvira returns home for Christmas, she senses the trouble in Melissa and tries to alert Daria, who remains oblivious to the depth of her daughter’s turmoil.
One day Melissa receives a call from Daniele, who promises a surprise and asks her to come over. There, Daniele and his friend Arnaldo coax Melissa into a threesome. Though initially reluctant, Melissa chooses to take control and explore her sexuality on her own terms. At school, Melissa’s diary—in which she records her sexual encounters—falls into the hands of a classmate who reads it aloud to others, including her friend Letizia Ciampa (Manuela). The exposure fuels a rift between Melissa and Manuela, who feels betrayed by the disclosure.
Arnaldo, Elio Germano, phones Melissa and asks her to meet him. He takes her to an underground basement where he blindfolds her and arranges for her to perform oral sex on him and four other young men. When Daria comes home and realizes Melissa is missing, she searches for her daughter, and soon learns of Elvira’s death after visiting the nursing home.
Seeking safety, Melissa goes to an older man she had connected with online, who enjoys being whipped. The encounter turns violent, scaring her, and she manages to escape to the nursing home where Elvira spent her last months. When confronted by Daria about the diary’s truth, Melissa confirms the writings are real, and the two share a tearful embrace as Daria apologizes for being oblivious.
On the final day of school, Melissa and Manuela reconcile their friendship. A shy, eccentric classmate named Marco, Nilo Mur, who has long admired Melissa, finally musters the courage to speak to her. He shows a notebook of sketches of Melissa, even drawing one last portrait before they share a light kiss on the cheek. Afterward, Daniele invites Melissa to a party at his place that night, and she tentatively agrees.
At the party, Melissa makes a bold choice and jumps off a cliff into the sea, emerging with a calm, almost content smile as her peers look on. Later, Melissa and Daria visit Elvira’s grave, bringing flowers and sharing a heartfelt, hopeful hug as they begin to mend what was fractured between them.
