The disappearance of her old friend, Lila Cerrullo, causes 60-year-old author Elena Greco to reflect on the early days of their friendship in 1950s Naples, when Elena and Lila are two very different girls at the top of their class. When the girls discover the lair of Don Achille, a criminal figure who controls the neighborhood, they decide to confront him.

As fourth grade draws to an end, Elena and Lila fight with their families for the chance to continue their education. Later, a trip out of town becomes a day Elena will never forget, and a death changes things in the neighborhood forever.

Now a teenager, Elena grapples with the onset of puberty, her studies, and her friendship with Lila, who now works in her family's shoe-repair store. After a library awards ceremony reveals what Lila has been keeping secret, Elena learns what her friend's grand plans might be. Lila takes a stand against the dangerous Solara brothers.

Entering high school, Elena vows to stay ahead of Lila, academically and romantically. Lila eschews a parade of suitors vying for her affection, choosing instead to focus on her ambitions in the shoe shop. Promising a better future for the neighborhood, Stefano Carracci invites Elena, Lila and their families over for New Year's Eve, but things take a dark turn.

Elena grows tired of Gino, while Lila rejects two potential suitors at a cost. A rare outing into the city turns violent. Elena worries about not being there for Lila after accepting an invitation to spend the summer away from the neighborhood and her family.

On the island of Ischia, Elena runs into the Sarratore family, reigniting her childhood crush on Nino, who is at odds with his father, the charming Donato. Back in Naples, Lila's resistance to Marcello's pressing courtship reaches a breaking point. On the day of Elena's 15th birthday, an unexpected encounter leaves her shaken.

Elena returns to Naples to find Lila has made a romantic connection with Stefano, despite the looming presence of Marcello. As Lila embraces a more glamorous life at Stefano's side, Elena warns her about what people are saying around the neighborhood. Later, in hopes of keeping up with her friend, Elena encourages one suitor and rebuffs the advances of another.

With sales of Cerullo shoes lagging, Stefano cuts a business deal with the Solaras against Lila's wishes. After Elena gets kicked out of a class for voicing her opinion, Nino encourages her to write an article for his magazine about her experience. Later, Elena and Lila get unwelcome surprises.

With Lila on her honeymoon on the Amalfi Coast, Elena struggles to handle school and her relationship with Antonio. When Lila returns with visible bruises on her body, the two girls revert to their natural closeness and Lila’s will to take revenge against her husband grows. Elena continues to be bewitched by Nino Sarratore’s charisma but chooses not to mention him to Lila.

Elena's relationship is threatened when Antonio discovers she has asked the Solaras' help to keep him from doing military service, while Lila remains rebellious in her marriage to the often-violent Stefano. After a photo of her is exhibited at a wedding dress shop in the center of town and becomes the subject of much gossip, Lila makes a bet with Elena about how the whole affair will end.

Upset that her picture is featured prominently in the new shoe shop Stefano is opening with the Solaras, Lila comes up with a creative solution to deal with the matter and enlists Elena’s help. Though Lila begins working at the Caraccis’ new grocery store, she continues to resent her husband’s business activities and the source of their income. Model student Elena invites Lila to a party at her teacher Ms. Galiani’s house; there, the two girls become acutely aware of the fact that they belong to ever more distant worlds.

At Rino and Pinuccia’s wedding, Elena accepts Lila’s invitation to go on holiday, provided the destination is Ischia, where she knows she’ll find Nino. On the island, Elena, Lila and Pinuccia begin to spend more and more time with Nino and his friend Bruno and Lila starts to take a strong interest in Elena’s summer reads. As Lila and Pinuccia exhibit signs of nervousness when their respective husbands come to visit for the weekend, Elena is thrown when Lila comes to her bedroom to make a confession.

As Pinuccia returns to Naples, a new secret excites Lila and numbs Elena, who nonetheless becomes embroiled in its coverup. Subdued by Lila's charisma and indifferent to Bruno's flattery, Elena finds herself the keeper of a far darker clandestine series of events involving Donato Sarratore. After the girls encounter Michele and Gigliola, who have come to Ischia on a day trip, Lila seizes the opportunity to throw the whole truth in Stefano's face.

Following her formative summer on Ischia, Elena throws herself into her studies and looks towards a future outside of the neighborhood. After a brilliant finals performance, Elena happens upon Lila, who is working at the shoe store and has grand plans for a fresh start. As Elena leaves Naples to commence her prestigious university studies in Pisa, Lila decides to leave Stefano and moves into a modest apartment, but the failings of her plan soon emerge.

Three years into her time in Pisa, Elena has developed into an elegant and cultured young woman – but still feels like an outsider. After a consequential breakup, Elena falls ill and is visited by her mother, who has come to nurse her back to health. During the night, Elena takes to reading Lila’s diaries, which were entrusted to her for safekeeping; in these tomes, Elena discovers Lila’s dedication to her new role in the face of Stefano’s increasingly violent behavior.

With graduation in sight, Elena is overwhelmed by memories of her past and copes by drafting her first novel. Meanwhile, she finds a new suitor in Pietro Airota, the son of an esteemed academic. After Pietro proposes, Elena entrusts him with her manuscript before heading back to Naples, where she reunites with her family and visits Ada, who updates her on the tempestuous events she's missed. Upon receiving some unexpected good news, she sets out to find Lila, whose circumstances have seen a dramatic change.