In Texas, a boy is cast into the desert. Under the relentless heat, he is to dig a hole each day for 18 months. Escape promises only death by thirst or the poisoned-tongued, yellow-spotted lizards. The object: to teach a bad boy to become good. In Dublin, his creator relaxes by a rain-spattered window. "It was always my idea from the beginning that it would be a fun book rather than a grim book." In the work of children's author Louis Sachar, all is humour and tightly layered. Setting is everything.

Holes is the story of Stanley Yelnats, wrongly banished to Camp Greenlake for being, as he constantly finds, "in the wrong place at the wrong time". His life was pre-determined by a curse placed upon his great-great-grandfather and now he digs, ever-fearful of the warden.

"It is not autobiographical," Sachar says. "I made it up as I went along." A slight figure in a thin woollen jumper, Sachar sits quietly in the hotel foyer, watching the world. He has a warm handshake and a cheerful demeanour. He is relaxed. He laughs at the observation - he has a cold and feels deplorable.

The author of 17 books, Sachar is at the height of media attention in the US. Holes has been a bestseller for two years and won the National Book Award for Young People's Literature in 1998 and the Newbery Medal in 1999. He has been questioned on everything, from the weighty morals of the book to the fairytales, but maintains that nothing was premeditated.

"For me, it was just trying to keep the story interesting." He derives enjoyment from reader-analysis but says: "Whatever morals there are, they were not ones that I set out to do. They were things I felt as I was doing it."

So where did the story come from? "I tried to find some idea that intrigued me. One thing I tend to do is write stories where the plot is not believable, but at the same time the characters react very believably. I came up with the setting and then the idea of digging holes under the hot sun. This thought came from my having moved to Texas. There was something appealing to me about all this useless work. Starting out, I just made fun of the whole concept."

But there is nothing humorous in the story for Stanley. The prose, in keeping with the boy's laborious, self-conscious efforts, is tight and restrictive. Sachar agrees that at times it was necessary to be compassionate towards his subject. "The first instinct you have when you put Stanley in the camp is to make all the other boys treat him badly. Instead, I thought that's just too much, so I made the other kids accept him."

Sachar appears as self-assured and as logical as the events in his book. "I like the idea of peeling things off layer by layer."

Married and with a teenage daughter, he lives in Austin, Texas. He was a lawyer but left the practice in 1988 after the success of his writing. At college in Berkeley he became a teacher's aide at an elementary school, because it was an easy escape from the sombre college atmosphere. It was there that he was inspired to become a children's writer.

"I keep the readers in mind when writing and make the language simple for them. I never sacrifice stories or ideas. I have to be careful, though, about what kids read." Stanley's torment is never terrifying. Sachar feels this is because children can accept the imaginary. "It is an unreal fear. It is the real-life fears I would keep out."

At 45, he has no plans for another novel. A family man, he expresses a concern for his daughter. "I've been thinking about her a lot lately. I think she resents it when people come up to her and say `your dad's my favourite author', because I'm her dad. I shouldn't mean so much to other kids."

A film of Holes is on the way: "They hired me as the screenwriter and then employed someone to polish it, which has me a little worried. I hope they don't change it too much."

He enjoys public reaction to his work. "Children love the puzzle aspect and how people fit together." Many adults have also read the book: "The way to get along in life is to treat adults like kids and kids like adults."

Holes by Louis Sachar is published by Bloomsbury price £5.99 in UK