Hulu and MGM will develop Margaret Atwood’s new novel The Testaments for the screen, the partners told TIME exclusively. Bruce Miller, showrunner for the Emmy-winning television adaptation of The Handmaid’s Tale, is involved in discussions about how to best approach the new material. It’s unclear at this stage what form The Testaments will take — whether it will be folded into the existing Hulu series or developed as a separate work.

Atwood, who appears on the cover of TIME this week, will release the highly anticipated follow-up to her 1985 dystopian novel on Sept. 10. The new book jumps forward in time about 15 years after the famously ambiguous end of The Handmaid’s Tale, where protagonist Offred boarded a van that would take her to an unknown fate. The first season of the Hulu series, which premiered in April 2017, stuck closely to many of the major arcs of the original novel. The finale ended with the same image of Offred facing uncertainty about her future as in the book. But as the show has continued — Hulu has picked up a fourth season — its writers have had to develop the narrative beyond Atwood’s original story.

The Testaments will help. The book is told not from the perspective of Offred, but instead from those of three other women connected to Gilead: a young woman raised in the oppressive society; a Canadian teen who learns she was actually born there; and Aunt Lydia, a major villain in both the original novel and the show. In season 3 of The Handmaid’s Tale, Lydia finally got her backstory — one that showed her grappling with romantic rejection and shame in her life before the regime took over. The new book takes an even deeper dive into her mind, one more conflicted about Gilead than it may appear on the surface.

Photograph by Mickalene Thomas for TIME

Atwood, who started writing The Testaments before the show premiered, has worked closely with Miller and his team on each season, advising on story plans, details about Gilead and aspects like character names. During a recent interview, Atwood recalled sharing some choice words with Miller when she learned Lydia was going to be stabbed by a vengeful handmaid: “You absolutely cannot kill Aunt Lydia, or I will have your head on a plate,” she remembers saying.

The show is widely acclaimed and has won 11 Emmys over its run so thus far, in addition to a Peabody Award and other accolades. But reviews of the latest season were more divided, with some critics and viewers expressing a sense of fatigue over the continual traumas depicted.

Atwood acknowledges the narrative strain. “They can’t keep Offred in Gilead for many more seasons, or a certain amount of wheel spinning will be going on,” she says. “They have to move her along — and I’ve given them lots of ways of how that would happen.”

Miller is looking forward to the release of The Testaments, since his staff has yet to read the closely-guarded book. He’s eager to hear which details his team finds most compelling and how they might incorporate or build up to those in the show. The new book, with its three different narrators, offers fresh perspectives on Gilead and how it works. “We’ve tried to hint at the wider world as much as possible in the show,” Miller says. “The Testaments really gives us much wider glimpses into other parts of the world.”

Write to Lucy Feldman at lucy.feldman@time.com.