Later that night, I put on my trainers and stuffed an old witch’s hat and a wand into a bag. My plan was to break into the school and find out if anything in Mrs Winkle’s magic box could help me solve the problem of Mrs Cuffy.

There just had to be all sorts of cool stuff in that box! Maybe there was a potion to make you invisible! Or a spell to make you fly! Everyone said I was too young to do all that stuff yet – but no one could stop me if I was on my own, could they?

Of course, Charlie wanted to come too. He wound himself around my legs, pleading with his round golden eyes.

‘No chance, Charlie,’ I said, wagging my finger at him. ‘This is not a job for a cat! You’d only try and gobble her up, you know you would!’

Charlie wasn’t a bit happy. He created a huge fuss, yowling and climbing up my legs.

‘Ow!’ I said. ‘Shh! You’ll wake the aunties!’

Eventually I shook him off, and he flounced into a corner in a sulk. I opened the window of my bedroom and climbed out into the night.

I made my way to St Munchin’s through the deserted streets. It was deathly quiet. I wished I was tucked up in my own warm bed like everyone else instead of creeping through the night like a burglar. How did I get myself into these situations?

St Munchin’s looked massive, black and scary at night. The black iron gates were locked, so I squeezed through a gap in the fence into the playground. I knew that one of the windows of the corridor had a broken catch, so I crept along, testing each window.

Every time a branch creaked or a bird flapped, it felt like my heart leapt into my mouth. A nervous sweat broke out on my forehead and dribbled into my eyes. Finally I found the right window and climbed through it into the school.

The school corridor was even spookier than the playground. There were no lights on, but a full moon shone through the windows. The jagged shadows of the trees swayed black against the wall. They twisted as if dancing to wild music that no human could hear …

I crept to Mrs Winkle’s room, held my breath and pushed open the door. My heart felt as if it was going to burst as I crept into her office and towards her desk.

There sat the silver box, glinting in a beautiful pool of magical moonlight.

I went to the top drawer in the desk. I opened it – and there was the silver key! I hugged myself in excitement and picked it up. I tiptoed to the box and slotted the silver key inside the lock. The box sprang open at once.

The box was packed to the brim with magical objects, tricks and spells. Most of the stuff was out of my league – I wasn’t even allowed to handle magic like this yet.

There was invisibility powder, giant finger bones for telling the future, magic dust, a mini-crystal ball, a dream kit, phials of dragon poison …

I picked up an open jar full of green goo, sniffed it and recoiled. Yuk! It smelt like a cross between old fish guts and rancid camel’s milk.

I looked at the label.

‘“Sorcery Slime”,’ I read aloud. Smelly Slime more like! I put the jar on the desk and continued rummaging in the box.

I was so busy rifling about, I didn’t see the extra shadow on the wall at first …

But at the back of my neck the hairs stood on end. A dark shape appeared in the corner of my eye. I stopped, turned around slowly and squinted. It was a shadow – and it was definitely growing …

What was it – a tree branch, a cloud? The shadow grew bigger still. This was no tree. It had whiskers …

‘Charlie? Is that you?’ I whispered. I crossed my fingers. Maybe he’d ignored my instructions and followed me.

Suddenly the air was split by a piercing scream. My blood ran cold. I’d heard that sound before – and it wasn’t Charlie!

Out of the gloom leapt the dark shape of Mrs Cuffy. She sprang onto the desk and fixed me with ratty little eyes full of hate. The next thing I knew, she had pushed me aside and jumped right into the magic box!

‘Get out of there!’ I shouted, trying to pull her out.

But Mrs Cuffy was surprisingly strong for a rat. She used one back leg to hold the box lid open and grabbed at the spells and potions with her two front paws. She picked up anything that came to hand – shrunken lizard heads, shark eyeballs, anything – and lobbed it at me.

There was nothing I could do except duck. I watched helplessly as magical objects whizzed out of the box, past my ears and all over the floor.

After about ten seconds, Mrs Cuffy’s head popped above the side of the box. Her whiskers twitched as she held up something in her front paws. It was a test tube filled with pink powder. This time, she took careful aim before she threw it at me. I ducked out of the way of most of it, but a tiny bit scattered on my feet.

To my horror, my feet immediately went numb. I stared down at them. Inside my trainers, they grew smaller and smaller. As I lifted each one up to look, my socks and trainers fell off.

My mouth dropped open. On each foot my five toes had turned into two big toes and one small one! I rubbed my eyes hard.

I no longer had human feet – I had pig’s trotters!

‘Where are my feet?’ I gasped. ‘Mrs Cuffy! What have you done to me?’

I don’t know if you’ve ever heard a rat laughing but it is not a pretty sound. Mrs Cuffy clutched her sides as her furry, bony rat-shoulders shook with high-pitched giggles.

Furious, I grabbed the open jar of Sorcery Slime.