Daniel Handler has written two novels for adults, The Basic Eight and Watch Your Mouth. Lemony Snicket has written seven books for children. They both live in New York City. But don't get confused; they are one and the same person. His name is Handler, his pen name for children at least is Snicket.

Snicket's success began in 1999 with The Bad Beginning: A Series of Unfortunate Events, the first gloomy instalment about the Baudelaire orphans: Violet, 14, Klaus, 12, and baby Sunny. When their parents die in a fire, the three precocious (but endearing) children find themselves homeless and relentlessly pursued by master of disguise Count Olaf (think Vincent Price, but nastier) whose only interest is the substantial inheritance Violet will get when she comes of age - providing she stays alive.

With each book, the children face a volley of perilous situations including Count Olaf's ploy to marry the under-aged Violet, a car accident, the gruesome death of Uncle Monty (poisoned) and Aunt Josephine (nasty accident involving leeches), and a string of traumatic situations that inevitably involve a silly but well-meaning adult doing a terrible job of protecting the children.

While Handler, 31, is delighted children enjoy his books, Snicket spends most of his time trying to put them off. "It is my sad duty to write down these unpleasant tales," he laments in The Bad Beginning, "but there is nothing stopping you from putting this book down at once and reading something happy, if you prefer that sort of thing." It appears many children don't prefer that sort of thing. They want what most adults want in a good book: plot, tension, love, death, suspense, intrigue and well-formed characters.

While the three Baudelaire siblings are brave and quick-witted, almost everything frightens Snicket. "That's what's so much fun: to write about such danger and yet it's narrated by such a profound coward." Handler says Snicket always "takes the path of least resistance" and suspects that's why children enjoy reading about him.

The book covers help, too. While Snicket's wicked prose is captivating, the look of the books makes them almost irresistible; hard-bound, petite, with thick paper and deckled edging, an old-fashioned book-plate and illustrated endpapers. The darkly funny illustrations by Brett Helquist add a wonderful dimension. So how did a conventional but unknown writer of adult novels turn into a star of children's books? Handler never intended to write for children, but when he submitted a manuscript set in a high school (The Basic Eight), an editor asked him to consider the idea. "I said no. I considered myself to be somebody who couldn't possibly write saccharine tales." In retrospect, he admits his response was unfair.

"I hadn't read any children's books since I was a child nevertheless I thought that was what the children's book industry would want." After much nagging, he agreed to an informal meeting with the editor. He brought a manuscript he'd abandoned a gothic story for adults that he suspected could be re-cast for children. "I thought I'd meet with her, tell her this idea and finally I'd get her off my back. I thought she'd say, 'You're right. You can't write for children.What was I thinking?'."

But the editor liked it. Although she anticipated a negative reaction from the publishing house, they ran it past "the gatekeepers of children's culture: librarians, teachers", who liked it, too. Handler says the success of A Series of Unfortunate Events is "really the story of the books failing to fail".

Critics, however, have accused Handler of writing overly melancholic books for the young. It seems some adults would prefer children took Snicket's advice and picked up Nancy Drew or Enid Blyton instead. "Recently someone said to me, 'You seem very talented, but you're writing these terrible books, why don't you write something like E.B. White?' I thought, do you mean the book where the little mouse is searching desperately for his parents and never finds them? (Stuart Little.) Or the book where the spider (Charlotte's Web) sacrifices herself to stop the butchering of the hero? They are dark stories and it's interesting to me that people remember these books as cheerful!"

As a boy, Handler felt more at home in a library than on a playing field. When his parents encouraged him to play soccer, Handler says, "All I wanted to do was sitin the middle of the field and space out. "After the game my father would pick me up and sometimes we would get ice-cream and sometimes we wouldn't. One day I suddenly realised it had nothing to do with how well I'd played or whether I was being a good boy in the car or anything like that it only had to do with whether my father wanted an ice-cream. "That's sensible enough no great tragedy but it was the beginning of realising that your good deeds weren't always going to be rewarded and your bad deeds weren't always going to be punished. The world was not always governed by the rules that were often being placed in front of you when you were a child." Handler says this moment of truth made him a "naturally suspicious" adult, an idea that has found its way into A Series of Unfortunate Events.

When the adult Handler sat down to write A Series of Unfortunate Events, he decided to write the books he would have enjoyed reading as a child. "I didn't do any market research and I didn't think I had a natural affinity to write for children. I tossed so many books across the room because I thought they were too cheerful. I started to think, what wouldn't make me toss a book across the room?"

So far, seven of a planned 13 books have been published and three of them have been on The New York Times children's bestseller list.

With success comes comparison and Handler jumps in quickly. "I'll bring him up first!" The "him", of course, is Harry Potter. Handler admits J.K. Rowling's success has permanently altered children's literature. He's pleased children's literature gets a lot of media attention and that "adults are thinking of the genre as something to be discussed and appreciated". He also believes the success of the Potter books means publishing houses are taking chances with experimental writers. "It's a great time to be writing children's books."

When he's not writing, Handler enjoys wandering around Coney Island. "Even in the 'on' season it feels like the off-season. All the broken-down carnival rides, the rollercoaster covered in ivy while spooky-looking people in booths sell food to nobody. It's a dying place." A perfectly morbid place for Lemony Snicket, too.

A Series of Unfortunate Events is published by HarperCollins.