WHAT DO you do when your favourite author doesn't write the ending you want? Or when you want to know what would happen if the hero went off with someone else? Quite simply, you write the story yourself. Fan fiction - fiction written by fans - is big. There are thousands of websites dedicated to the genre - and they aren't all Harry Potter. Local teenagers Cheung Ying-Wah, Amato Lo and Clara Me got a taste for it last year when they were waiting for the release of the fifth Harry Potter book, Order Of The Phoenix. 'Fan fiction is for when you miss the real thing so much, you need something to read when you're waiting for the author to come out with their next book,' says Ying-wah, 15. But for Amato, 16, fan fiction is often better than the original: 'Sometimes you don't get what you want in the real thing. Like I wanted Harry to be paired up with Hermione. J.K. Rowling didn't make it happen, but it's there in some fan fiction,' she says. One of the biggest fan fiction sites is fanfiction.net. It has a huge collection of fan fiction, including books (more than 150 titles, from Judy Blume and Peter Pan to Bridget Jones's Diary and even the Bible), movies, television shows (Friends, X-Files), comics, cartoons and games. For die-hard Potter fans there is fictionalley.org, where Harry finds himself in situations J.K. Rowling never dreamt of. Almost all the stories have disclaimers saying that they are not stealing the author's work. Some of the disclaimers are amusing in themselves. Take the one on the Potter site which reads: 'Disclaimer - I don't own any characters. Shame really. Imagine how rich I would be if I did!' Or the one on a Stephen King site: 'I live in my own world, and I'm proud of it. None of these people are mine.' The Internet has allowed the sites to be truly global, and many operate in several languages. Fanfiction.net has stories in 11 languages, including Chinese, Japanese and Russian. The sites create a community feel, with message boards, forums and even review panels. The fans do not get paid for their writing. They usually do it because they want to explore different aspects of a character or story, because they enjoy writing - and because they are fans. Clara, 15, started writing fan fiction a year ago. She focuses on her favourite author, Tamora Pierce, and Japanese cartoons. 'Most of the people writing fan fiction are 15 to 18 years old - and they are serious about writing. I've been in contact with writers from the UK, Taiwan and Singapore,' she says. Most of the sites recommend that the writer finds someone to read over their work before they submit it. This person is called a beta-reader. The story is usually then read by an editor before it is published on a site, but some sites are less strict about this. Through bulletins and message boards, fan fiction writers have created their own jargon. A 'Mary Sue', for example, is when the writer tries to put themselves into the story. 'It's usually easy to spot Mary Sues. They are usually new characters with impossibly good qualities, and they start pairing off quickly,' says Ying-wah.