To Catriona, who told me to stop daydreaming and start writing – and gave great feedback and advice. To Liam, for putting up with my stressy, can’t-do-it moments, and Calum and Caitlin, who endured many dinners of peanut butter on toast and were such excellent first readers. Thanks to Mum, Dad, Andy, Lori, Mary-Jane, Fiona, Helen, Kirsty, Sheena, Zarah and all my brilliant friends – for believing in me, even when I didn’t. Also to Dr Gill Russell for help with the starry stuff, and to Dr Shelagh Neil for advice on the medical bits.

Thanks to Tallulah and Roxanne, whose enthusiasm helped me to find the best agent in the world, Darley Anderson, and also to Lucie, Julia and everyone at the agency. Last but not least, thanks to Rebecca, Francesca and the whole fab team at Puffin, for making the dream come true.

I never sleep, the night before my birthday.

It’s not the usual kind of excitement – I don’t get all wound up about whether I’ll get a new CD player or a pair of rollerblades or a guitar. It’s a guitar, anyway – Dad told me.

I’m not stressed out about a party or a sleepover or a trip to the ice rink, either. We have this tradition, Dad and me. We stay home with a takeaway and a video. If it’s his birthday, Dad picks Indian food, along with something hippy-dippy or all-action to watch, like Lord of the Rings or Star Wars. When I was little, I used to go for Disney, then soppy stuff like The Secret Garden or Fairy Tale. This year, we’ve got Sky TV and I get to have complete charge of the remote control all evening. I’ll probably just skip between MTV and Kerrang!, munching pizza as I flick.

Birthdays are pretty cool, I know. It’s just that, no matter how hard I try, I can’t relax, I can’t not care – and I’m always a little bit scared the night before. Every year, I’m up at dawn watching for the postman, because there’s one very special card – a parcel, even, sometimes – I just have to get.

It’s the only day of the year I hear from her.

When I was five, I got a postcard from Kathmandu. It had a picture of a Buddhist temple with a pointy golden roof and weird, staring eyes painted beneath it, and the message was written in three colours of felt pen with loads of kisses.

When I was six, there was a postcard of a donkey with flowers in its mouth, and the postmark said West Cork, Ireland. The next year I got a proper birthday card and a handmade rag doll with pink and purple hair made from fluffy yarn, and a dress stitched from somebody’s old tie-dye T-shirt.

On my eighth birthday, there was a postcard from Marrakesh in Morocco, a picture of a grinning Arab girl with armfuls of gold bracelets. The next year I got a rainbow-striped hat with a floppy brim and a postcard of a castle in Wales. I wore the hat every day, till the edges got frayed and the colours ran in the wash. Then I stuck it to my pinboard, along with the postcards and the photos, and it’s still there now.

When I was ten, I got a dreamcatcher, a circle of willow criss-crossed with a crazy spider’s web of bright threads and beads. Soft, white feathers hung down either side, with some tiny bells in the middle. The postcard (a spooky stone circle in Wiltshire, this time) told me to hang the dreamcatcher over my bed. Its magic web would catch all my bad dreams and melt them away, so I could sleep safe and deep, all night long. Wish I’d had that when I was five.

Last year, when I was eleven, she sent a silver chain with a tiny chunk of rose-quartz crystal hanging from it. I always wear it, even at night. There was no postcard that year, just a letter. It’s the kind of letter that’s difficult to read, even now, but also the kind of letter I needed to have a long, long time ago. It said that she loved me, that she was sorry, and that one day we’d be together again.

I rolled the letter up, tied it with a strand of purple yarn from my moulting rag doll and put it in my treasure box. Then I stuck the envelope to my pinboard, so I could see her loopy, gel-pen handwriting and