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With its adolescent heroine who discovers her mystical abilities after encountering an other-worldly protagonist, Cassandra Clare's bestselling Mortal Instruments series seems like a clever combination of J.K. Rowling and Stephenie Meyer's iconic creations.

But with a movie now in development, it won't be long before the New York-based writer's enthralling work about demon-hunters in contemporary New York City is recognised as very much its own distinctive beast.

"People will always compare you to the most popular book in your genre at the time," says Clare, 37.

"When I began writing the books it was Harry Potter, and as I went on it became Twilight. All books feed on the same genre elements. There's a lot of ancient biblical mythology in my books and we all use the same kind of classic mythology at the heart of all our stories so there are bound to be similarities."

Born in Tehran and raised in California, Clare spent time in Switzerland, France and England as a child.

An ardent reader of classic folklore, she discovered contemporary urban fantasy writers such as Charles de Lint, Ellen Kushner and Terry Windley, who all contributed to the Borderland anthologies.

"When I was growing up in the 80s there was a sort of cult movement of writers who were popularising this idea that you should bring fantasy into the modern world," she recalls.

"For me, that was much more relatable than traditional high fantasy, which was all very medieval with castles and knights.

"I couldn't connect with that as a 12-year-old girl but I could connect with the idea of children or teenagers running away from the real modern world to join a semi-magical world.

"A lot of the stuff I read back then featured fairies and vampires but I wanted to do something with gods, demons and angels. That was my big idea at the time."

After moving to Los Angeles to attend high school, Clare visited her grandparents in New York every summer holiday.

"I found it to be a fascinating and magical place," she says.

"I was there at the right time in my life for it to feed my imagination and allow me to create fantasies about the places that I was in."

As an adult, she moved permanently to New York in 2001. "That was when I started working on the books as I reconnected with my New York roots," says Clare, who based her character Clary's home on her own apartment in the Brooklyn suburb of Park Slope. "Where Clary's stepfather Luke lives is where I lived when I first moved to New York and didn't have any money so I had to live in Williamsburg, while the Institute is on the Upper East Side where my grandparents lived," she says, referring to the Demonhunters' hidden headquarters.

"I like the idea that different neighbourhoods have different personalities and can lead to different kinds of magic."

After reaching a dramatic conclusion in her third novel, City of Glass, Clare intended to continue Clary's story in a series of graphic novels. However, when those plans fell through, she turned her comic-book plots into a new sequence of three novels, beginning with the just-published City of Fallen Angels.

"It starts a bit after the end of the last book," she says. "It doesn't function like something like Harry Potter where you have one through-line story running through all the books. It's one trilogy and then a second trilogy. I think of it as almost like two seasons of a TV show where you have a complete story and then you have a second complete story about the same people."

After City of Glass, Clare embarked upon The Infernal Devices, a prequel to The Mortal Instruments, beginning with Clockwork Angel before continuing with last year's Clockwork Prince.

"I'd been spending a lot of time with the same characters and as a writer that can start to feel a bit claustrophobic. It's been good for me to alternate the two series."

Set in London in the Victorian era, The Infernal Devices is inspired by her childhood experiences living in the British capital for two years. "I fell in love with it," says Clare. "I didn't go to school so my parents would give me assignments to do all around the city. I would write up what I learned and I found out lots of fascinating details. So when I decided to do a corresponding series to the initial series that I had created, London was a natural fit. It has had a wonderful history for such a long time and it has a secret past that's no longer there but lives on in our imaginations."

The story centres around 16-year-old American Tessa Gray who inadvertently stumbles upon a shadowy netherworld of vampires, warlocks and other supernatural creatures.

"London is a much older city than New York, which is partly why it takes place 130 years in the past," she says.

The Infernal Devices' final instalment, Clockwork Princess, is due to be published at Christmas and the fifth Mortal Instruments, City of Lost Souls is scheduled for May next year.

But after the sixth book, City of Heavenly Fire, is published in two years, Clare will finally bring the series to a much-deserved close.

Clare is looking forward to coming to New Zealand for the first time next month, where she will be a guest at the Auckland Writers & Readers Festival alongside Australian fantasy authors Margo Lanagan and Garth Nix and our own Elizabeth Knox.

"I love her writing on Vintner's Luck and her work for young adults," she says, referring to the Wellingtonian's Dreamhunter duet. "Her work is very unique."