hat's Lionboy about?
It's about a boy called Charlie, who can talk Cat. He comes home one evening and his parents aren't there when they should be, and one of the cats he knows tells him they've gone off. It turns out they've been taken, because they've discovered something, and he has to find out where and why. He ends up on this giant circus ship and makes a deal with the circus lions: he'll help them escape if they help him rescue his parents.

ow did you come up with the idea for the story?
Mum found it growing in the compost heap, all cold and sad and lonely in its little coat, so she brought it in out of the rain and now its blossoming.

ow long did it take you to write?
Well I didn't do much of the writing - Mum does that. The whole thing started with bedtime stories when I was about three, in 1996, so that's seven years ago, but Mum's written lots of other books since, so it hasn't taken all that time.

ave you always been a budding writer?
No, I used to be a baby. But I have always liked writing stories, except at school when you have to do them really quickly and tidily with no spelling mistakes.

hat advice would you give to other girls who want to write a bestseller?
Read loads of good books. Then read loads more. Then write your story. (If possible get a parent to do the typing). Then read more. But don't pinch ideas, that's cheating.

hat was it like working with your mum?
It didn't really seem like work - we'd just chat and have ideas and talk about what the people are going to do next, and how they feel, and whether there should be another shipwreck and should we bring the whale in yet and what we want in the circus. Then mum writes it all down and I read it and tell her if it's any good. Lots of things get into the book - Mum's boyfriend Robert wrote some tunes for my lizard Zizu and they ended up in the book too - they're the circus music and it's printed in the book so you can play it. And there's a Ghanaian nursery rhyme that my Grandma knows. And there are some really good maps and diagrams.

id you have many arguments about what happens next?
Only one - she wants to kill somebody off and I won't let her. I say 'Somehow I doubt it' and she laughs. We haven't sorted that one out yet. I don't know who's going to win.

ow did you feel when you found out the book is going to be made into a film?
All fizzy inside. But then someone said 'don't count on them making the film till you're putting on your outfit for the premiere'. That doesn't stop me planning what I'd like to wear though. I hope we'd be allowed to go on set, if they do make it. We're both script consultants but nobody has consulted us yet. The person writing the script wrote the script of Edward Scissorhands which is a very good film. Everybody should see it.

ho would you choose to play Charlie?
We do play fantasy casting but I don't know any young boy brown actors. Maybe my friends' brother Akin. He's not a professional actor but he was the Robin Hood character in our school play of Shrek. Otherwise some African English boy newcomer. Someone good. I can't even say 'Will Smith as a kid' because he's too funny...

re you working on your next book yet?
We've written book two of Charlie, and we're on the way with book three. After that we might do Tigergirl and Leopardlad and Cheetahchild and Pumaperson… or not. Mum wants to write a brilliant grown-up novel and win the Booker Prize, so I might have to do one on my own - but I'll be a teenager by then so I'll probably be too busy with homework and sulking. Or I might just want to go to bed.

f you could design a roller coaster, what would you call it?
Frightwig.

hat other books do you like to read/what are your favourite books at the moment?
Jacqueline Wilson, Garth Nix, Eoin Colfer, Edward Eager, Malorie Blackman, Philip Pullman, Ann Brashares, Meg Cabot... lots and lots.

ho do you admire (author/poet or otherwise)?
I admire Edward Eager who wrote Half Magic and The Well Wishers.

f you met them today, what would you say to them?
I didn't know there was a prequel to the Well Wishers, and can I have your autograph please? I'd like to meet Nelson Mandela too but I don't know what I'd say to him.

hat was the strangest place you ever stopped to read a book?
I don't stop to read; I just read books while I go. The strangest place I've ever read a book is probably on my skateboard. Going along.

hich book most inspired you and why?
The stories about Amazing Grace by Mary Hoffman and Caroline Binch: Amazing Grace, and Grace and Family, because Grace is so like me and does lots of things that I've done like go to visit her dad's family in Africa.

an you tell us a bit about your inspiration for Charlie and his gift for speaking cat?
Mum and I are both allergic to cats so it's a bit funny - but there are two cats in our street who I love, Missy and Freddie, and sometimes they understand when I talk to them.

f you could speak cat, what is the one question you would most like to ask?
Meeow?

Photograph © Justine Stoddart