Elena Ferrante’s My Brilliant Friend inspired a kind of instant devotion that rarely greets literary novels these days. The frenzy only accelerated with the publication of the subsequent books in her Neapolitan Quartet, which traced the fraught friendship of Lila and Lenù from the girls’ impoverished childhood in 1950s Naples through to middle age. (Two of the four books were named to The New York Times’ recent list of the 100 best books of the 21st century—one at number 80, the other at number one.) The fact that Ferrante published the books under a pseudonym only added to the mystique.

When HBO announced a TV adaptation, some fans worried it would be a pale imitation of Ferrante’s prose. Yet the series became as much of a critical darling as the books. Italian director-screenwriter Saverio Costanzo, handpicked by Ferrante herself, succeeded by remaining faithful to the spirit of the novels while also conjuring a rich televisual world for Lila and Lenù. That involved a wild casting process (the producers auditioned almost 9,000 Neapolitan children) and the construction of an elaborate, 215,000-square-foot set that stood in for the girls’ dilapidated neighborhood.

Over the show’s first three seasons, the girls forge a bond that is both delightful and destructive. Even as their paths diverge—Lenù leaves Naples and becomes a famous writer, while Lila stays behind, tamping down her dazzling intelligence—they remain locked in an emotional tug of war. As Ferrante herself once told VF, female friendships “are a terra incognita, chiefly to ourselves, a land without fixed rules.”

The 10-episode final season of My Brilliant Friend will finally debut September 9 (at 9 p.m. ET) on HBO and will stream on Max, picking up more or less where the season three finale left off: in the 1980s, set against a turbulent backdrop of political violence and social upheaval in Italy. All 10 episodes are directed by filmmaker Laura Bispuri, who aimed to bring a naturalism and emotional intimacy to the show’s last chapter. A new cast was also brought in to replace the show’s young stars Margherita Mazzucco (Lenù) and Gaia Girace (Lila), who played the girls in the first three seasons. Stepping into their shoes are Alba Rohrwacher (La Chimera, Happy as Lazarro) as the bespectacled intellectual Lenù (now mostly known by her full name, Elena) and Irene Maiorino (Gomorrah) as the mercurial Lila.

Rohrwacher isn’t a dead ringer for Mazzucco, but she felt like a natural choice to the creators because she’d been doing adult Elena’s voiceovers since the first episode of My Brilliant Friend. Costanzo declares Rohrwacher “a great actress, maybe the greatest we have in Italy,” and says that even if she doesn’t look exactly the way viewers have come to see Elena, “Alba knows her soul.” Maiorino, on the other hand, looks very much like a grown-up version of Girace. “But she somehow delivers a different version of Lila, without her freshness,” says Costanzo. In the past, “Lila was blackmailing everyone with her beauty, which is her weakness—because in my opinion she never really believed in herself as much as Elena did.”

The third key member of the revamped cast is Fabrizio Gifuni as Nino Sarratore, Lila and Elena’s schoolmate turned roguish intellectual. Nino has had intimate relationships with both friends; at the end of the third season, he lured Elena away from her husband and children. “Fabrizio is really courageous, because to be Nino Sarratore in the fourth season after we know how much he’s hated by everyone, this is a real challenge!” Costanzo says with a grin. “You see, through Fabrizio, what it means for a man not to be able to be what anyone expected him to be. I know how much effort he put into loving this character, which is not easy—to make him human, to make it real.”

Costanzo began developing the series in 2016. Almost nine years later, he still hasn’t met the mysterious Ferrante. “In the first season she wrote the scripts with us,” he says. “I asked her opinions about some actors, and that wasn’t the right choice. She’s not a director and she has her own image [of characters], so it’s hard for a writer to be involved. Also, she’s kind of a ghost, so you cannot really have a discussion with her.”

Ferrante continued to collaborate on scripts, but this season she was a bit less involved. Costanzo speculates that it’s because Bispuri, a woman director, was at the helm of the series. “I remember when Maggie Gyllenhaal made The Lost Daughter, Maggie told me Ferrante sent her an email saying, ‘Whatever you do, it’s okay because you are a woman, and I respect what you have to say.’” This attitude encouraged Bispuri to make her own creative mark on the season. “Laura was free to experiment with the show’s grammar, and I really liked the way she did it. She doesn’t want it to look like anybody else, she wants to be herself,” Costanzo says, comparing it to the way Elena’s character forges her own literary style. “This is exactly the story of My Brilliant Friend.”

Season four finds Elena struggling to integrate the disparate elements of herself. There’s the poor little girl who spoke a rough Neapolitan dialect; the ambitious feminist writer who made a name for herself in the intellectual circles of Milan; the wife and mother trapped in a prison of domesticity; and the sensual creature seemingly willing to give everything up for her childhood crush, Nino. Is Nino just a pawn in Elena and Lila’s relationship, or something more? Costanzo suggests that originally, Elena needed Lila “to be her energy, her fuel”—it was Lila’s own writing that first inspired Elena to become an author, after all. “Once she’s free from Lila, she needs Nino to be her fuel. Maybe in order to have the power to write a book like My Brilliant Friend, she needed to prove herself and to be seen by him. This is the kind of mystery that draws these characters to each other.”

Early in the new season, Elena says as much: “Even though by then I wrote and thought only about women’s autonomy, I didn’t know how I’d do without his body, his voice, his intelligence.” This is a major conflict for Elena in season four, according to Bispuri: “She’s writing about feminism, but in her personal life there is the problem of Nino.” He is what we’d now call a fake feminist ally. “I think that Nino is the most feminist thing that Ferrante did in the books, because I know a lot of women in my personal life—intellectual or not intellectual—who believed in men like Nino Sarratore. I think when you see this season, every woman will recognize this kind of man.”

Lila, meanwhile, is busy sabotaging herself in other ways. While Elena starts out as a weak child who grows into her power, Lila begins as a force of nature who grows increasingly fragile as an adult. “In this season, she builds a little industry in the neighborhood around computers,” Bispuri says. Lila also becomes further entangled with the Solaras, the local Mafia thugs who have haunted the girls since childhood.

The series may be an unsentimental journey, but for those behind the scenes of the show (not to mention those who watch it), it will be hard to say goodbye to the women of My Brilliant Friend. “When you lose somebody that was so important to you, that person stays with you,” Costanzo says. “My Brilliant Friend taught me things I didn’t know about myself. I am the person I am now thanks to Elena, Lila, and Elena Ferrante, and I believe so many readers around the world feel the same. They will never forget them and what they experienced through them.”