For the rest of Friday, I wandered about St Munchin’s in a dream. I got told off in class by Mrs Cuffy for staring out of the window. Later in the playground, I got thumped by Donna Delaney and her gang for walking through the middle of their skipping game.

Mary was no help. As we plodded into class after break, she rubbed her hands together and did a high-pitched witchy cackle.

‘Hubble bubble!’ she screeched. ‘Toil and trouble!’

‘Ha ha, very funny,’ I grumbled.

I kept thinking about Verbena’s wicked, grinning face. How was I was going to stop her from kidnapping my best friend – even though that friend could be very annoying? Why was I always getting myself into stupid situations?

I hardly slept at all on Friday night. I kept staring out of my bedroom window at the moon, nearly full and glowing brightly …

I spent all of Saturday cooped up in my room with Charlie, turning page after page of Advanced Magic. I could hardly understand a word of it. It was complete gobbledegook. Finally, I shoved my old witch’s hat on my head and tried a spell. I made a star shape on the floor with some string.

‘Charlie,’ I said, ‘Come here a minute.’Ü

Charlie jumped off my bed, arched his back and stood inside the star with me. He gazed up at me with trusting golden eyes. I read out the rhyme:

The only soggy thing I had was an old tissue up my sleeve so I rubbed that on Charlie’s head. I wasn’t about to start catching live mice so I gave Charlie some chocolate ones instead.

Then I stood inside my star, chanted the spell and waited for the magic power to flood through me and into Charlie.

But all that happened was that I stood there until my legs went to sleep, while Charlie ate too many chocolate mice and was sick in my trainers.

Meanwhile, the hours and minutes ticked away. I tidied my room, hid Advanced Magic in the wardrobe, and kicked my witch’s hat out the door. I put the disgusting, vomit-y trainers in the washing machine and waited. There was still no sign of Mary …

At long last, there was a knock on the front door and I heard the patter of Wormella’s feet in the hall.

‘It’s all right, aunty!’ I shouted. ‘It’s for me!’

I raced downstairs and flung open the door.

‘Hi!’ said Mary. She was carrying a giant bottle of fizzy drink. ‘Sorry I’m late. Mum said I had to clean out my room or she would ground me for a month.’

‘Never mind, you’re here now,’ I said, pulling her through the door. I had a quick look around outside. All was quiet.

‘What first?’ I said. ‘TV or pizzas?’

‘Pizzas!’ shouted Mary. ‘Yee-hah!’

The rest of the evening passed doing normal sleepover stuff. We did our nails, watched a movie, played games on my computer, and stuffed our faces. We got into our pyjamas and spent ages talking about everything we could think of.

All the talking helped me to forget about my problems for a little while, but Mary still noticed something was wrong. She cocked her head on one side and gazed at me.

‘Anna, are you OK?’ she said. ‘Why do you keep looking out of the window?’

‘It’s nothing,’ I said, closing the window and locking it. ‘It’s just a lovely full moon tonight, that’s all.’

‘You look scared, though,’ said Mary, sitting cross-legged on her sleeping bag.

Her voice dropped to a whisper.

‘It’s not the witch again, is it? The invisible one? The one that no-one can see, except you?’

Then she burst out laughing and shoved some more crisps in her mouth. I forced myself to laugh too, and clobbered her with my pillow.

But as the night went on, I got more and more jumpy. Butterflies were dancing in my stomach. I kept expecting to see Verbena’s green face floating at the window, licking her pointy teeth.

‘It’s late,’ I said, at last. ‘We’d better get some sleep.’

‘OK,’ said Mary. She snuggled down in her sleeping bag on the floor, yawning. ‘I love sleepovers!’ she said.

‘Yeah, they’re great,’ I mumbled.

Soon Mary was snoring, but I still didn’t slide down into my sleeping bag. Instead I sat bolt upright with my back against a chest of drawers. I was going to stay awake all night and make sure nothing happened to Mary.

‘Come on, Charlie,’ I said. ‘You can help me by sitting on my lap and digging your claws into me whenever I yawn, OK?’

Charlie miaowed and leapt onto my lap.

The minutes ticked slowly by, and my eyes began to feel heavy. I looked down at Charlie. He was sound asleep.

‘Fat lot of help you are!’ I said.

I lifted him off and got up to open the window. Some fresh air would wake me up. I leant on the windowsill, breathed in the cool, clean smell and gazed at the magical full moon. It was so beautiful …

My head felt heavy. My eyes kept closing all by themselves. I was determined to stay awake – but surely it wouldn’t hurt if I put my head down on my arm for just a minute?

I laid my head on my arm and Charlie crept back onto my lap. I felt warm and floaty …

Suddenly a mad screech ripped through the air near my ears! My head shot up and I forced my eyes open.

Green fog was streaming through my window. Outside, hovering side-saddle on a broomstick, was Verbena.