Praise be! The news that Margaret Atwood is to write a sequel to The Handmaid’s Tale has been greeted enthusiastically by fans, to judge by the response on Twitter, where the prize for most obvious gag must go to Stephen Colbert, who said: “Margaret Atwood is writing a sequel to The Handmaid’s Tale, and Donald Trump is almost finished with the prequel.”

Atwood, of course, got there before him. In her press release, she announced that one of her two points of inspiration for The Testaments, besides the questions from her readers, was “the world we’ve been living in”. But you can’t help the suspicion that there’s a much bigger galvanising influence going unmentioned here, and whether, without that, fans would have been more ambivalent about the author’s decision to revisit Gilead 35 years after Offred’s story ended on its famously equivocal note.

Because there is already a sequel, one that happened outside Atwood’s control. The Emmy-winning Hulu series killed the ambiguity that makes the original novel such a haunting, nuanced read by returning for a second season, in which the misogyny and violence against women were ramped up so far that many women I know stopped watching after the first few episodes – feeling that it had abandoned the moral universe of the book and descended into meaningless torture porn. In one of her record sell-out events at the Hay Festival earlier this year, Atwood was carefully neutral about the adaptation and its continuation of her story, damning it with the faintest of praise. “I would have to be awfully stupid to resent it, because things could have been so much worse,” she said, before pointing out reasonably that you can’t have a second season in which the main character either dies or escapes to freedom.

Others were less generous; the New York Times called season two “dutifully brutal” and complained that it “gave in to every one of the show’s most tedious instincts”. No wonder Atwood wants to claim her own narrative back; what better way for an author to express their critique of someone else’s sequel than by writing the definitive one? When a fan on Twitter responded to the announcement by saying: “Hope it’s based on the wonderful book – not based around the plot of Hulu’s second season,” Atwood – who engages enthusiastically with readers on social media – replied: “Fear not. It is a surprise.”

Margaret Atwood, who will be 80 next autumn when the book is published. Photograph: Murdo MacLeod/The Guardian

But is there an argument that writers should not tinker with their best-loved works, particularly once those have become classics? Not everyone greeted yesterday’s announcement with joy. “What a hideous error,” responded New York Times book critic Charles Finch. “Writers, leave your work alone! Henry James showed you what happens!”

JK Rowling frequently draws fire from fans for speculating on how her characters may or may not have turned out: when she mused in a 2014 interview that she probably shouldn’t have had Ron and Hermione end up together, forums exploded with outrage.

But, as any author will testify, there are some characters you just can’t leave behind, especially those that established your reputation. For 35 years, Atwood’s choice to leave Offred’s fate hanging in the balance has been an essential part of the novel’s meaning. Keen-eyed readers may think they spot linguistic clues scattered through the text – that is all part of the game. The power is handed to the reader: you decide, Atwood seems to say. Now, thanks to the TV adaptation, that decision no longer belongs to her readers, and so it is right and proper that Atwood herself gets to assert what really happened next.

There is also the changing political landscape that demands a response. The Handmaid’s Tale has sold three million copies since the presidential election of 2016, and spent 88 weeks on the New York Times bestseller list; most authors can only dream of a second wind like that after three decades, but perhaps not the circumstances that provoked such a revival of interest. Atwood could not have anticipated, in 1984, that in 2017 women at protest marches would carry banners saying: “Make Margaret Atwood fiction again!”, or that Offred’s red robe and white bonnet would be adopted at protests across the world as a symbol of women standing against the erasure of so many freedoms gained during the past 35 years. And yet the novel predicts exactly this: that our modern liberal democracies are only a few legislative changes away from repressive regimes, that every right we hold dear could be taken away with one election.

It’s unquestionably time to revisit Gilead; not only for Atwood, who will be 80 next autumn when the book is published, to have the final word on those characters, but to hold a mirror up to our own times. Let’s hope that, by then, the world she depicts is on the way to becoming dystopian fiction once again, a timely reminder not to let the bastards grind us down.

• Stephanie Merritt is a novelist and feature writer