“Drat this thing. It won’t go in. “ Pip seized the bag of punch pads by its handle and yet again tried to squeeze it into the storage cupboard. At least three-quarters of the space was already taken up with boxes.

“I’ll do it!” her sister Immy shouted, jumping up and down. “Let me have a go! I don’t have a big bum like you!”

“No, you’re just a pain in the bum,” Pip sighed, crawling out. “Go on then.”

Immy started to push, eyes squeezed shut with effort.

“Don’t touch that disc on the door!” Pip warned.

Immy folded her arms against her chest and stuck out her chin. “You are SO bossy. So what if I touch that wheel thingy? What’s going to happen? Blast off?”

Pip peered at the wooden disc nailed to the back of the storage cupboard door. It did seem harmless enough. About the size of a dinner plate, it looked like a pie chart, with bright slices of colour arranged around a black circle in the centre. In the middle of the circle was a wishbone, embedded deep in the wood. It was about the length of a carrot, though. Too big to belong to a chicken.

She shrugged and gave the bag one last, hard kick. Finally, it went in. Just as she was about to close the cupboard door, Immy hopped forwards and swiped at the disc with her forefinger.

“Imogen – no! It might be an antique, that thing.” Pip slapped her hand out of the way. Immy lifted a hand to slap back, then froze. Her eyes widened.

Now, Immy was the kind of little girl who would come downstairs gabbling about zombies climbing through the window or splat-shaped monsters seeping out from underneath her bedroom door. Pip knew from long and weary experience what her sister’s fake fear looked like: the quiver of amusement at the edges of her cute lips, a gleam of mischief in her big eyes. This time was different. Her skin had paled. Her dark brown curls were quivering. She pointed at the door of the cupboard. “Look!”

Pip looked. She held her breath.

Something was pouring from the red slice on the disc. Rusty liquid, perhaps? But there was no sound of rushing water. Heart pounding, she bent down to take a closer look.

It was dust. Bright red dust.

Immy reached out to touch it as it fell. “It’s warm,” she whispered. “Like it’s been in the sun.”

The dust was forming a little pile on the floor beneath. Pip’s mouth ran dry and she swallowed hard. To her astonishment, powder began to fall from some of the other slices too: white, brown and blue.

Pip yanked at the loose ends of her red belt in frustration, shaking her head at Immy. “Why do you always have to mess with things that aren’t yours?”

Immy tilted her chin up in defiance. “What makes you think you’re in the clear? You were staring at it like a dumbo.”

“Shut it, rat bag,” Pip muttered. She rubbed a knuckle above her right eyebrow. It was that headache again, the one she always got when she felt panicky and stressed. She hadn’t had one like this for a long time, though. Not since they got the call from the hospital about Gran.

The four piles of dust were now about the height of an adult’s hand. Pip laid the tips of her fingers on the peak of the red one. She left five oval dips which quickly filled out again when she drew her hand away. The dust smudged on her sweaty skin and flowed down her palm in a long scarlet trickle.

“What’s happening?” Immy demanded, jumping up and down on the balls of her feet.

“You tell me.” Pip patted the disc lightly with the palm of her hand, searching for a button or switch. The wood was warm to the touch, just like the sand. She realized the pie slices were not painted on, but made up of tightly compacted powder, like one of her mum’s eyeshadow palettes. But how come only four of them were shedding?

She bit her lower lip. “I suppose there’s some kind of mechanism inside it. There must be a way to stop it…”

“Pip?” Immy tapped her on the shoulder.

“What now?”

Immy pointed down, her finger quivering.

Two of the piles on the floor were gone. The blue and the red ones were still intact, but a shimmering pool of murky brown was spreading on the floor, its edges like paper held over a flame.

Pip shook her head. No. This could not be happening. Not to her. She didn’t even believe in magic for Pete’s sake. At least not the kind that existed beyond silly conjuring shows with wands and bunnies and girls in glitzy leotards getting sawn in two.

The dust was moving quickly, about the speed of a scuttling spider. Pip grabbed her sister’s hand and backed away from the cupboard.

Immy yanked on her sleeve. “There’s…there’s something up there too.”

Pip’s eyes flickered upwards. A cloud of white hovered above them. It already covered half the ceiling, contours shifting, sinuous as a shoal of fish.

The sweat on Pip’s forehead had turned a deathly cold. She smacked a hand against her head. Come on, Pip. Think.

She had to get out of the corridor and shout for their instructor Olly in the hall. He’d know what to do. He always did.

But just as she was about to run for the door, the cloud dropped. In an instant, the girls were surrounded by thick, shimmering dust. Pip opened her mouth to scream, but it was as though she had inhaled smoke at a bonfire. She began to splutter and cough, eyes streaming.

Immy’s choking and wailing shocked her into action. She seized her sister’s shoulders and pushed her towards the door.