The hammer rang once. A spark jumped off the anvil and did not go out. It waited. They followed.

It skipped across the Green and into the print shop. It stopped on the long table, next to a square of paper.

"Fold me, I won't mind," said Kami.

"Somewhere with a puzzle," said Inkling. "A really good one."

"Then start with a half," said Kami. "And then half of that."

They folded Kami in half, edge to edge. Then they folded it in half again. A small thick rectangle, four layers deep.

The last crease went flat, and the paper opened like a door.

It was bright. That was the first thing. Winter sun poured through high windows.

They stood at the end of a very long, very wide hallway. Metal lockers lined both walls. There was a drinking fountain and a notice board covered in coloured paper. It smelled of floor polish.

"America," said Kami softly. "California. A school, in January 2002."

A boy sat on the floor in a hoodie. In his hand was a small, hard, lumpy square of paper. He was frowning at it.

"I'm Sam," he said. "Tomorrow is big-question day in my class. My grandpa says nobody in the whole world can fold a piece of paper in half more than seven times. I want to fold one eight times and show him."

"How many have you done?" asked Inkling.

"Six," said Sam. He pushed at the lump. "It won't bend any more. It's like folding a brick."

"I'll do it!" said Lan. "I promise. Put it on the floor. I'll stamp it flat, and then it'll fold."

She put the lump on the floor and lifted her foot.

"Stamping only tears paper," said Mark. He caught her sleeve just in time. "Then you'd have two pieces, and that doesn't count. Read the drawing first."

Lan put her foot down, on the floor, next to the paper. Her ears went hot.

"I promised before I checked," she said. "Sorry, Sam."

On the notice board, between the coloured papers, someone had taped a drawing. It showed a long strip of paper, folded in half, then again, then again. Under each fold was a number.

Mark read it carefully. "Read the drawing before your hands move," he said. "Every fold doubles the layers. One becomes two. Two becomes four. So every fold is thicker than the last."

"Like a brick," said Sam.

"And a thick fold needs more paper to bend round," said Mark. "Your square ran out. You need paper that is long. And thin."

Sam ran to the school office. He came back with a whole roll of thin paper, the kind that comes out of a cash register.

They unrolled a long strip down the hallway, longer than two classrooms.

"Bring it all the way over," said Cornelia. "End to end. Exactly."

Sam walked one end all the way back to the other end. Fold. Two layers.

"Point to point, then hold," said Cornelia. And again, the same way. Four layers. And again. Eight.

"Three folds," said Inkling. "Eight layers." She had counted first.

They folded the fourth time. Sixteen layers. The fifth. Thirty-two.

The sixth fold was hard. Sixty-four layers did not want to bend. The ends slid apart and did not meet.

"It's ruined," said Sam.

"Crooked is just a first go," said Crinkle. "Smooth it out and try again. The crease remembers."

Sam opened the sixth fold. This time Sam held one end and Lan held the other. They walked the ends together, slowly, until they met. Then they folded.

Sixty-four layers. Six folds.

"Hold it still," said Presso. "Now press it flat. Press slowly, press firmly."

Sam folded the seventh time. It was hard work. Presso knelt on the packet and pressed until it lay flat.

"A fold you press is a fold that stays," said Presso.

"A hundred and twenty-eight layers," said Inkling, counting on her fingers in twos. "Seven folds."

The packet was fat and stiff. Everyone sat back. Grandpa was right after all, thought Sam.

"I'm still one piece of paper," said Kami quietly. "And there is still enough of me to bend round. One more."

Sam looked at the packet. It was still long enough to fold, just. He pushed with both hands. Slowly, slowly, the packet bent over. He pressed it flat himself.

"Eight folds," said Sam.

"Two hundred and fifty-six layers," said Inkling, who had worked it out first. "Every fold doubles."

"Every fold makes me something new," said Kami.

Sam took out a pencil and wrote his new rule for Grandpa: Every fold doubles. The more folds you want, the longer the paper has to be.

Far down the hallway, a teenage girl and two grown-ups had unrolled a very long strip of thin paper, much longer than theirs. The girl folded it again, and again, the same way every time. She did not stop.

Lan found a plain square in her pocket. They unfolded it flat, and the door closed behind them.

The spark dimmed to a warm dot and settled back on the anvil. The Green was just the Green again.

Back on the Green

At the print shop, Lan took a strip of paper and folded it in half, three times. She counted the layers out loud: one, two, four, eight.

Tell the story back to someone. How many layers did eight folds make?