Next morning, I got up early and crept around the house like a ghost. I could not let Aunty Grizz and Aunty Wormella see my horrible new feet, so I made my breakfast and got ready for school before they were up.

I jammed my feet into my wellies and wedged socks inside. Then I limped to school.

St Munchin’s was in chaos. The new-style mutant rat was popping up all over the place and scaring everyone half to death. Mr Cuffy was stamping around in a fury, laying down poisoned traps and shouting at everyone.

‘I’ll kill that monster!’ he roared. ‘I’ll get it, if it’s the very last thing I do in this world!’

Owen Brady’s gang had come to school armed with home-made catapults. Every time there was a rustle behind a door or a table, they fired off soggy paper pellets.

They never hit Mrs Cuffy, of course – she was far too quick for them – but they hit each other and dozens of other kids. By lunchtime, the sick room was full to bursting with a steady stream of bruised, snivelling children.

Meanwhile, Mary and I flopped around like two wet rags. We were so tired that we couldn’t take in anything. Luckily the school was in such an uproar that no one noticed. No one said anything about my wellies and we got away with doing nothing all day.

When the home-time bell rang, Mary lifted her head off her desk and woke up a bit.

‘At last!’ she said. ‘So, are we going rat-hunting or what?’

‘Sure you still want to come?’ I said.

She shot me a withering look.

‘Someone needs to keep an eye on you, don’t they?’ she said. ‘Have you got your witchy kit with you? Let’s have a look!’

I put my fingers to my lips. We waited until the last person had left class then I opened my bag.

‘One black pointy hat,’ I said. ‘One genuine witch’s wand, and one book of brilliant spells.’

But Mary was difficult to impress.

‘That magic book looks a bit dog-eared,’ she said, poking at it. ‘Your hat’s got a hole in it and your wand is bent!’

‘It was all I could manage at short notice,’ I said. ‘Come on, let’s go!’

We slipped out of class and followed the gravel path out of the school grounds to the bottom of the Cuffys’ garden.

The big school bins were there all right. They were overflowing with rubbish because the bin men hadn’t been for a week – and, boy, did they stink!

‘Here, ratty, ratty!’ called Mary, holding her nose. ‘Come on, there’s a good girl!’

‘She’s not a puppy, Mary!’ I said. ‘And we’ve got to be quiet. She’s dangerous, remember!’ But Mary just giggled.

We searched around the bins. It was gross. The lids wouldn’t close because there was a week’s worth of rotting school dinners spilling out of the top of each bin. Flies and wasps buzzed around our heads as we poked around.

Suddenly Mary made a strangled sound, grabbed my arm and pointed upwards to the top of one of the bins.

Sure enough, there she was – Cuffy the monster rat!

Crouched on a pile of green, mouldy sausages, she looked even more enormous by daylight. She was gnawing hard at the rotting meat, and the black bristles on her greasy tail stood on end in pleasure.

I nudged Mary and put my finger to my lips. I opened my bag as quietly as I could, lifted out my witch hat and jammed it on my head. I whipped out the wand and spell book. I threw away the bag.