By Caroline Briggs
BBC News entertainment reporter in Cannes
British author Anthony Horowitz has been lauded at the Cannes Film Festival, where the movie rights to his book Stormbreaker have been sold to Hollywood.
Mr Horowitz wrote TV show Midsomer Murders before creating Alex Rider
An international hunt is now under way to find an actor to play teenage super-spy Alex Rider in the Stormbreaker film.
Mr Horowitz's six books about Rider's adventures have sold millions of copies around the world.
The US rights to the $40m (£22m) movie were snapped up by Hollywood film moguls Harvey and Bob Weinstein at the festival this week, and the pressure is on to find the right boy to fill Alex's boots.
And they are pretty tough boots to fill. Mr Horowitz said the actor must be able to scuba dive, rock climb, shoot and be adept at martial arts as he battles international terrorists with an array of gadgets to rival James Bond.
And while admitting it is a tall order, Mr Horowitz told the BBC News website the film's success rests on making the right choice of who plays Alex.
"This is the scary thing. Here you have a $40m film, possibly more, with everything resting on that choice. It's critical," Mr Horowitz says.
"The film opens in a classroom with the teacher reading out Alex's name.
"As soon as that boy's eyes reach the camera, fate is sealed. The whole film depends on it."
The search to find Alex has been likened to the hunt for Daniel Radcliffe, who plays Harry Potter in the films.
But while Rowling had an idea of the type of boy she wanted to play the boy wizard, Mr Horowitz says Alex is harder to define.
"There are certain aspects of Alex that are critical, but they are abstract. He has to be cool and he has to have a street-wise quality.
"He doesn't have a scar on his forehead and he doesn't wear wire-rimmed glasses, so there is no prototype there like there was for Harry Potter."
Mr Horowitz is due to start writing the seventh Alex Rider book in 2006
"All I know is that he has got to be 14-years-old, drop-dead good looking, fit and be a good actor. We know he is out there somewhere."
Producers have seen 700 boys so far and Mr Horowitz has been shown clips of a dozen.
"I'm not saying some of those boys aren't still being considered but, for me, I haven't seen him yet. I'll know it as soon as he walks through the door."
In the books, Alex becomes the youngest agent in the Special Operations Division of MI6 when his uncle is killed on a secret mission.
Alex outsmarts terrorists with an array of gadgets including bionic spot cream and a missile-launching bicycle.
Mr Horowitz, who created TV series Midsomer Murders, admits the world's most famous spy led him to create Alex.
When Roger Moore wore a safari suit in Octopussy, Mr Horowitz concluded James Bond had become "less cool than he used to be".
"To be cool, you have to be 14 years old," he says. "A 14-year-old on a snowboard is cool. A 14-year-old's dad on a snowboard is just sad."
And like the James Bond films, there are plans to turn the novels into a lucrative franchise if Stormbreaker is a hit.
Due to begin writing a seventh Alex Rider book next year, Mr Horowitz says he is not too concerned at losing control of the character he created.
"It is inevitable that a film is going to change a book and the writer is going to lose a large amount of control," he says. "But as soon as you sign it away, there is no resisting it.
"I have asked myself if it would have been better to resist the film itself, but a film will attract more readers to the book, and as an author, that's what you want."
Mr Horowitz will also stay closely involved with the movie. As well as writing the screenplay, he is also working with the director Geoffrey Sax.
But he admits the Weinstein brothers are "very much the power behind the film" now.
"It's only beginning to hit me how big this is turning out to be."