Brains are funny things. Some are tidy, like a row of sharpened pencils. Others are steady, like a tortoise plodding down a garden path.

Then there’s Max Fletcher, he had a brain like popcorn.

Not the well-behaved, sit-in-a-bucket kind you eat in the cinema. Oh no. Max’s brain was the wild microwave kind. The kind that escaped the bag, leapt across the kitchen, and smacked you straight in the eyeball.

POP! A goldfish on a skateboard.

POP! A toilet that sang opera when you flushed.

POP! POP! Glow-in-the-dark shoelaces and a custard sandwich.

POP! POP! POP! A potato talk-show host called Mr Mashington.

And that was all before breakfast.

Now, you might be thinking, Well, how marvellous! A boy full of ideas. But too many ideas are like too many Brussels sprouts. Exciting at first. Then a little queasy. Max’s mum had long ago stopped asking,

“Where do you get these ideas from?”

Because the answer was always, “My brain.”

And Max’s brain was about as well-behaved as a classroom full of chimpanzees armed with water pistols.

At this particular moment, Max was supposed to be thinking about fractions.

And, if you’ve forgotten, fractions are teachers’ clever way of making pizza sound boring. A third of this. A quarter of that. Half of something else. Very unfair on pizza.

But Max wasn’t thinking about pizza. He was thinking about helicopters. Specifically, helicopters delivering pizzas so enormous they needed seatbelts.

“Max Fletcher!” snapped Mrs Figgles.

Mrs Figgles was his teacher. Her eyes were so sharp they could slice cheese. Her voice was so sharp it could slice you.

Her perfume smelled faintly of cabbage and despair. “What is three-quarters plus one-half?”

Max considered this carefully.

POP! Helicopter pizza.

POP! Broccoli invasion.

“Well, Miss,” he began cheerfully, “if it’s pizza plus broccoli, the answer is disgusting.”

The class howled. Mrs Figgles did not. She looked like someone had force-fed her a lemon. With the peel still on.

“This is mathematics, not MasterChef!” she snapped. “Although,” Max continued sweetly, “if you did put broccoli on pizza, it might count as one of your five-a-day…”

“Enough!” Mrs Figgles slammed her ruler on the desk. Snap! The poor ruler broke in two. She stared at it like it had betrayed her, then shoved the pieces into the bin.

Beside Max sat Maya Chen, his best friend.

Maya was very good at drawing and very good at sighing. She was doing both now. On her page: a doodle of broccoli marching across pizza like tiny green soldiers. Next to that: a goldfish on a skateboard.

She slid it to Max without looking.

He exploded with laughter. “That’s exactly what I was thinking!”

“I know,” Maya sighed. “That’s why I draw them. Otherwise, you’ll never shut up.”

Now, between us, Maya secretly liked Max’s popcorn brain. She’d never admit it out loud. She pretended he was a nuisance and, to be fair, he was, but she liked doodling his explosions of nonsense before they smashed into everyone else’s heads.

Mrs Figgles loomed over them. “Max Fletcher. Give me one good reason why you should not be moved next to the bin.”

Max thought. Thinking made more popcorn.

POP! “Because, Miss, the rubbish would whisper its secrets to me.”

Mrs Figgles blinked. “What?”

POP! “Crumpled worksheets. Banana skins. Sausage rolls. They’ve all seen things. Heard things. Do you really want me to become… the Bin Whisperer?”

The class collapsed into laughter. Mrs Figgles nearly did too.

“Back Row. Now.”

So Max trudged to the back row, grinning. Because sitting near the bin wasn’t a punishment to him. He liked bins. They were mysterious. Sometimes they held treasure. Sometimes rats doing long division.

It was then he spotted it.

On the board, written in green marker:

Welcome New Headteacher Tomorrow

Max tilted his head. Very odd. He didn’t remember Mrs Figgles mentioning it.

“Maya!” he hissed.

She craned her neck. “So?”

“So,” Max whispered, “a new headteacher means one of two things. Either: a) boring, or b) an evil wizard who collects children’s toenails in jam jars.”

Maya rolled her eyes. “Please tell me you’re not going to think about this all night.”

“Too late,” said Max cheerfully.

And pop! went a brand-new kernel in Max Fletcher’s popcorn brain.

The school bell finally rang. Children stampeded like rhinos out of the gates. Maya and Max walked together, bags bumping against their legs.

“Did you really tell Mrs Figgles you could hear the bin whispering?” Maya asked.

“I didn’t tell her,” said Max. “I warned her.”

Maya groaned. “You are a walking warning sign.”

They passed the noticeboard again. The same green marker words stared down: Welcome New Headteacher Tomorrow. Someone had drawn balloons around it. Someone else had added a moustache.

Max squinted at it as though it might suddenly blink. “Maya,” he said gravely, “if the new headteacher is an evil wizard, we’ll need a plan.”

“We do,” Maya agreed. “The plan is: you do your homework and keep your mouth shut for once.”

“I prefer plans involving custard,” Max replied.

At the corner, they split, Maya heading up towards the flats above the shop that sold suspicious sausages, Max towards his terraced house with a letterbox that occasionally bit postmen’s fingers. Only a little. They usually get them back.

“Bye, Popcorn Brain!” Maya called.

“Bye, Chief Doodler!” Max shouted back.

At home, Mum opened the door holding a wooden spoon like a weapon. “Shoes off. Homework before tea. No experiments.”

“No experiments?” Max repeated. “What if the experiment is homework?”

Mum gave him “The Look.” Every mum has one. It says: I love you very much, but if you explode anything in my kitchen I will sell you to the circus.

Max sighed and flopped at the table. His maths book lay there, full of fractions. Ugh.

He stared. His brain fizzed.

POP! Seven custard creams minus three hungry seagulls.

POP! Pizza slices marching in formation.

POP! A singing toilet divided into quarters.

He picked up his pencil and wrote:

“If you cut a pizza into 8 pieces and eat 7, that is 7/8, unless the last piece runs away screaming.”

He added legs and a terrified face to the slice.

“Homework,” Mum called from the kitchen.

“It is homework!” Max protested. “The pizza slice is demonstrating velocity!”

“It’s demonstrating nonsense,” Mum muttered.

Later, at dinner, Mum plonked down stew that looked as though it had lost a fight with a swamp. Dad bravely kissed her cheek. “Looks hearty.”

“It’s experimental,” Mum said.

“You told me no experiments,” Max pointed out.

“Grown-up experiments are allowed.”

They ate. If you closed your eyes and thought about chips, it almost tasted like chips.

“So,” Dad asked, “how was school?”

“Educational,” Max said. “I learned that if you snap a ruler, Mrs Figgles snaps you with her eyes.”

Mum frowned. “You didn’t snap your ruler again, did you?”

“No, she did,” Max said quickly. “Also we’re getting a new headteacher tomorrow.”

“Oh?” said Mum. “Why?”

“Probably because the old one exploded.”

“Max…” Dad warned.

“Or joined the circus. Or retired to a volcano. Anyway, I’ve been thinking, what if the new one steals our ideas? Then we’ll all be boring!”

Mum ruffled his hair. “No one can steal your ideas, love. There are too many. They’d get squashed on the way out.”

Max laughed, but a wobbly feeling settled in his tummy.

That night, Max lay in bed, staring at a damp patch on the ceiling shaped like Australia. His brain was still fizzing.

POP! A headteacher with spaghetti hair.

POP! A headteacher with a pet tarantula called Mr Fluffkins.

POP! A headteacher who made everyone eat slugs.

POP! A headteacher who was… nice.

That last thought was the strangest of all.

He sat up, grabbed his Official Investigator’s Notebook, and wriggled under the covers.

He told himself very firmly that he wasn’t making a plan.

Which, of course, meant he absolutely was.

First of all, he’d need a torch. Or maybe three torches taped together, because you never knew when evil wizards preferred to lurk in shadows.

Then a coat hanger tied to a bit of string, obviously, for climbing out of windows.

A disguise would help too. Nothing too fancy. A moustache drawn on with a felt-tip would do nicely.

And biscuits. Always biscuits. Custard creams, at least two, although one of them might mysteriously vanish before the mission began.

Max yawned and scribbled furiously. His writing sloped downhill, as if even the words were tumbling into adventure.

“And Maya,” he whispered into the dark. “Definitely Maya.”

Because, as everyone knows, if you’re going to face a possibly evil, possibly toenail-collecting new headteacher, you need your best friend armed with a pencil, ready to doodle evidence.

Max peered out of his window. The street-lamps hummed.

A fox trotted past like it was late for an appointment. Somewhere a baby cried, probably because someone had fed it broccoli.

His stomach did a wobbly flip. Tomorrow looked big and strange and exciting, like a fairground ride you weren’t quite sure you were tall enough for.

He hugged his notebook, rolled over, and whispered into the dark:

“Tomorrow, we pop carefully.”

His brain, being his brain, popped anyway.