When Isabel Greenberg’s third graphic novel begins, it is July 1849. A young woman with a pugnacious jaw and a pair of unflattering spectacles on the end of her nose is striding out across a moor, oblivious both to the damp underfoot – the book’s first frame shows nothing more than a ladylike boot splashing through a puddle – and to the looming clouds above. Tiny in her bonnet beneath the vast, steely sky, this woman, for all her determination, strikes the reader as terribly alone.

And she is alone, for this is the writer Charlotte Brontë. In the course of the past year, she has lost all three of her living siblings – Anne, Branwell and Emily – to tuberculosis; she is still deep in grief. But then something strange happens. No sooner has she spread a blanket over the heather, and taken off her bonnet, than a dashing fellow suddenly appears beside her. He is not dressed for the moor. He wears a top hat, a scarlet cravat, dazzling white breeches and, somewhat incongruously, a pair of sunglasses. Who is he? Is this peacock with the spiky, rock-star hair real, or is he a figment of her imagination?

In fact, he’s the latter – though as Greenberg points out, in the case of the Brontës, reality and the life of the imagination are sometimes difficult to separate. “In Charlotte’s diaries, there’s a bit where Anne and Emily are sitting at the kitchen table, talking about baking bread or something, and then they just switch into what’s happening in Gondal as casually as if they’re discussing the weather,” she says.

Gondal was Anne and Emily’s imaginary world: an island in the north Pacific. Like Angria, the rival land invented by Charlotte and Bramwell, the older of the siblings, it had its roots in the Glass Town Confederacy, a realm that was inspired by the 12 wooden soldiers given to them as small children by their father, Patrick.

Facebook Twitter Pinterest A view of the moors near Haworth. Photograph: Christopher Furlong/Getty Images

“Their devotion to [Gondal] is extraordinary,” says Greenberg. “At times, it’s almost like an addiction – and this is what I wanted to explore in my book: the idea that the imagination can impinge on reality in ways that are both positive and negative.”

Charlotte’s moorland visitor, we will soon discover, is Charles Wellesley, the brother of Arthur Wellesley, AKA Zamorna, the most important character in Angria – and out on the moor, he now asks her if she wouldn’t like to visit Glass Town, which is all that remains of these lands since she abandoned them, for one final time. What follows is a wild journey: an odyssey that takes in both Glass Town and Haworth, the West Yorkshire village where the Brontës grew up. In Greenberg’s hands, it is both comic and tragic; a feat of narrative concision that is by turns dreamy, and gritty. If it’s a fantastic comic – and I think that it is – then it’s also one of the best books about the Brontës’ juvenilia ever written.

Has she always been interested in the Brontës? “I read Jane Eyre and Wuthering Heights at school,” Greenberg says, when we meet one cold winter morning. “I liked them, but I wouldn’t say I was obsessed. I didn’t know anything about their juvenilia until much later, but when I did finally hear about it, it interested me immediately from a world-building perspective. They were so young – and the sheer quantity and scale of it. It’s Tolkien-level.” Determined to dedicate her next book to it, she travelled to Yorkshire, hoping to see the tiny handmade books the Brontë children devoted to Gondal and Angria (they’re in the collection of the Parsonage Museum, where they once lived). “The first time, I didn’t have the proper paperwork. But the second time, I lucked out: a visiting American academic had them out already, so I was able to see a couple at last.” However, it was visiting Haworth itself that was most inspiring: reaching it across the moors on a local bus; the lingering sense of isolation. “It’s a special place. Not even all the tea shops can change that.”

Back in London, she read and read. “I got into a pickle. The more I researched, the more attached to the source material I got. Eventually, I had to stop and make some choices. The biggest decision was to choose which of their worlds to go for. My gut was to go for Gondal, with its amazing female characters.” She took the characters she thought most interesting, and some of the details of their plots. But thereafter, she freewheeled, adapting and embellishing the narratives as she thought fit. “Zamorna is as he appears in their stories, but the connections between the other characters, and the timeline, are my own. The Brontës were children of the empire, and there is a lot of Victorian racism in there, so I gave one of their black characters a more empowered story.”

Facebook Twitter Pinterest Pages from Glass Town. Photograph: Courtesy of Isabel Greenberg/Jonathan Cape

Did it feel at all transgressive, daring to rewrite them like this? “I would never have messed with Jane Eyre or Wuthering Heights. But these stories aren’t sculpted, and they weren’t intended for publication: if I was going to mess with anything, it was this.” She used the older, grieving Charlotte as a framing device. “There are lots of flashbacks, and to avoid confusion, I used colour to help the reader with the time frame. The present day [when Charlotte is alone and looking back at her childhood] is in sad blues and greys; the sepia tones signify flashbacks; and the Glass Town stories are in full Technicolor.” Charles, meanwhile, functions as Charlotte’s male alter ego: “That’s why they bicker a bit. Sometimes, he’s like a brother; sometimes, he’s more like some louche journalist.”

Greenberg, who is 31, studied illustration at Brighton University, and for an MA in animation at the Royal College of Art. She now teaches on the illustration course at Camberwell College of Arts, London. She still believes, however, that she owes her start as a writer of long-form comics to the Observer/Cape graphic short story prize, which she won in 2011. This, she says, made her career. “I felt so lucky. At the time, I didn’t have any commissions. I was working as a nanny. Winning it changed everything. It got me my first agent, and my first publisher.”

Her first graphic novel, The Encyclopedia of Early Earth, which came out in 2013, was nominated for two Eisner awards, and won the best book category at the British comic awards. Her second, The One Hundred Nights of Hero, made the New York Times graphic books bestseller list. What makes this all the more gratifying is that she didn’t grow up reading comics. “I didn’t know writing them was even something you could do,” she says. “I wanted to write, and I wanted to draw, that’s all.” For Glass Town, she completely changed her working practice, switching from black ink to pencil and charcoal: “a scratchier finish”. Having relied heavily on narration in her first two books, this one also makes more use of the comic form – something she would like to play around with in the future.

Comics, she notes, are becoming more mainstream, readers coming to understand that they are a medium, not a genre. But for those who create them, they’re also all-engrossing; the sheer labour involved is incredible. Thanks to this, she says she will always have to teach, and take on other illustration projects (she’s currently finishing a children’s book). “They’re never going to be the only thing I do,” she says, with a rueful smile. “Unless someone wants to buy the movie rights.” But this hardly matters. When she’s at her drawing board, they’re what she loves to do best of all.

• Glass Town is published by Jonathan Cape (£18.99). To order a copy go to guardianbookshop.com. Free UK p&p over £15