Perhaps there is something of the night about her, suggests Samantha Shannon.

Although the model-tall 21-year-old is certainly scarily talented, with a complexion that is a whiter shade of pale, sinister she is not - even if her extravagant imagination does veer towards the macabre and the grotesque.

I had called debut novelist Shannon - "the new JK Rowling," of which more later - to ask about the results of her finals at Oxford University, where she's been reading English at St Anne's College. She got a 2:1, as she'd predicted when we met recently in London. Not bad going for a student who spent all her time between lectures writing an ambitious, 466-page fantasy novel that is tipped to topple Stephanie Meyer's Twilight series from the bestseller lists. She may even give Suzanne Collins, author of The Hunger Games, a run for her money with her breathtaking book, The Bone Season.

It's about to be published in 18 languages, and the film rights were fought over by three major Hollywood studios. Lord Of The Rings actor Andy "Gollum" Serkis's Ealing-based Imaginarium Studios won out because, she says, "Andy really 'gets' it!" However, Shannon tells me, the most thrilling news is that she gained a first for her paper on Emily Dickinson, with whom she's as besotted as she is with John Donne - her "muse" for The Bone Season.

"I think I am of the night," is Shannon's response to my query as to whether she's been basking in July sunshine, in west London where she was born, grew up and still lives with her mother, stepfather and nine-year-old half-brother. I ask because Shannon has been known to spend 15 hours a day closeted in her bedroom writing. (When she was 15 and writing her first novel, the "not very good" unpublished sci-fi epic Aurora, her mother pleaded with her to get some fresh air. "She just wanted me to get some sun on my vampire skin.")

Heatwave? What heatwave? She's been indoors for weeks, writing furiously because she's bursting with ideas for the second book in what the blogosphere is calling her Clairvoyance Chronicles.

There are certainly no roses in her cheeks when we meet at her publisher's London offices, although she surely turned pink with pleasure when she landed a six-figure deal for the first three books of her projected series with Bloomsbury, publisher of JK Rowling's Harry Potters. Of "the Harry Potter generation," Shannon was obsessed with the books as a child. "I was 11 when Harry was 11. The challenge was to read them in a day. So when Harry Potter And The Order Of The Phoenix came out, it was like this big," she gestures a doorstop. "I had the biggest bags under my eyes because I read all night; I was paranoid someone was going to spoil it for me."

Like Rowling, she's invented her own world of fantasy and adventure to be spread out over seven books, although there the comparison ends. "The new JK Rowling? Definitely not," she insists. When the news broke about her publishing deal - "I was gob-smacked, the most surreal moment of my life!" - there was a media frenzy. "All this stuff on Twitter saying, 'Who the hell does this girl think she is saying she's the new JK?' I didn't say it, a Sunday Times journalist wrote it, then it was picked up by the Daily Mail," she sighs.

"There have been stories saying I'm a multi-millionaire. I wish! It's been extremely daunting because there will never be another storyteller like JK Rowling. Or another Harry Potter. What an odd expectation. It must be so annoying for her. I respect her work and love it so much. Of course, all the hype has drawn attention to my book, but now online reviews are being published and people realise it's very different stylistically from Harry Potter."

Set in a dystopian London, with a government called Scion in power in 2059, The Bone Season has a 19-year-old clairvoyant heroine - Shannon was 19 when she wrote the novel, which "just poured out in a great rush in six months". Paige Mahoney is "a dreamwalker" who works in the criminal underworld, based at Seven Dials. She doesn't crack safes - only people's minds, stealing their innermost thoughts and secrets.

It's a world in which clairvoyance is a crime; Paige commits treason simply by existing. Captured and kidnapped by the secret police, she's taken to a penal colony that is not a million miles removed from Oxford. There, the enigmatic Warden becomes Paige's keeper. Beauty and the Beast?

"Absolutely," agrees Shannon. "The book has echoes of lots of fairytales as well as the poetry and speculative fiction I love." Her literary influences range from Margaret Atwood's The Handmaid's Tale - "the book that awakened me as a feminist" - to Dickinson, Donne and Orwell. Inventive wordplay is one of the many pleasures of The Bone Season. "I knew I wanted to use slang after I read A Clockwork Orange," she explains, although she knew she could not sustain an argot as Anthony Burgess does in his great dystopian novel.

"But I wanted the world I'd created to have linguistic colour and it was a way of making Paige's voice unique since the book is written in the first-person. I've used Victorian slang - such as the mildly offensive 'bleached mort' for a blonde. These anachronisms led one person at Bloomsbury to describe my book as 'penny-farthing futurism', which I love. I've also taken words from modern colloquial English and created new ones. That slang is known as 'Cassie's Cant', from Cassandra, the oracle, and is used only by clairvoyants. But I'll clarify this in further books," she promises.

Everyone asks Shannon if she's clairvoyant, whether she saw her success coming. "Definitely not!" she exclaims, adding that she doesn't even dream though she'd love to. Her creativity probably owes more to the fact that she suffers from crippling migraine headaches, which influenced the visual milieu of her novel. "I think everything I write about auras comes from the visual interference you get with migraine when you think you're going blind. I'm sure that's where the spiritual dreamscapes came from."

The story behind her book has all the elements of those dreams she never has. While she was writing Aurora, her plumber stepfather met someone while playing golf, who mentioned that he knew the literary agent David Godwin. When Shannon finished the book, she sent it to Godwin. He rejected it. As did nine other agents. "I was devastated," she recalls.

But Godwin sent generous feedback and, during the long vacation, she got an internship at his office in Seven Dials, where seven London streets meet. She was lunching in a cafe in this odd corner of the city when she got the idea for The Bone Season. "I've always been intrigued by the number seven - then clairvoyance popped into my mind," she recalls.

She went back to university, did "mountains" of research into clairvoyants and began writing in secret, creating an anachronistic world where people dress in Victorian style while frequenting oxygen bars and using data pads. Then the renowned Scottish novelist and critic Ali Smith delivered a series of lectures at Oxford.

"My tutor said Ali was willing to look at any writing we might have. I was so nervous, but Ali read it then she looked at me and said, 'This is wonderful.' She was so full of praise. I couldn't stop babbling, then I burst into tears and phoned Mum, who had no idea I was writing another book. It was so lovely after the drama and heartbreak over Aurora. Then David read it and he took it to Bloomsbury ... After all those years of failure, I was numb."

So, has she blown her advance on that six-figure sum?

"I'm really frugal, very careful with money," she confesses. "I've a student loan to pay off anyway. My mother said I should buy a car, but I don't want one. I've just started paying rent - I have an office under the stairs in my parents' home. However, I am going to save up for a place of my own."

Does she never stop writing? Surely she sometimes goes out and has fun with friends?

"Not really," she responds. "I was never much of a going-out girl. I grew up with my nose in a book. Now I'm the weird writer in the corner. As for boyfriends, I'm 'married' to my books. I suppose I'm looking for a Warden since I'm so in love with him - he's the one character I transferred from Aurora. But I do have fun with my close friends, a great group. A good night out for us is actually a good night in, watching The Apprentice and eating pizzas."

The Bone Season is published by Bloomsbury, £12.99. Samantha Shannon is at the Edinburgh International Book Festival on August 22 and 23.