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 underground lair of Don Achille, a criminal figure who controls the neighborhood, they decide to confront him, facing their fears together and laying the cornerstone of a lasting friendship and rivalry.

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. As the girls’ encounters with the opposite sex become more and more frequent, 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. Things escalate quickly during a fireworks faceoff with the Solaras, leading Lila to see a new side of her brother Rino.

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.