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 cold this time," said Inkling. "With a fire, maybe."

"Then start with a cup," said Kami. "Something warm to hold."

They folded Kami in half, corner to corner. They folded the two side corners across. They folded the top flaps down. A little paper cup.

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

It was cold. That was the first thing. Then there was the smell of old books and a hissing radiator.

They stood in a long room with dark wooden walls. Tall windows had tiny panes of glass. Outside, yellow leaves were falling.

One pane had been mended with a new strip of lead. Beside it, someone had scratched a tiny hammer on the frame.

"America," said Kami softly. "Princeton, in New Jersey. The year is 1939."

A girl in a knitted hat sat at a long table. In front of her lay three small crayon drawings: a moon, a fish and a star. Beside them was a folded card, still blank inside.

"I'm Rosa," she said. "It's my little brother's birthday. I want him to find a surprise. But a card only has two sides, a front and a back. I have three pictures."

At the far end of the table, a young man in a grey sweater was folding paper. Next to his notebook lay a neat stack of long, thin strips.

"He cut those off his notebook paper," said Rosa. "He says American paper is too big for his English binder. He saves the strips."

The young man slid one strip toward them. Ten triangles were drawn on it in pencil, pointing up, down, up, down.

"I'll do it!" said Lan. "I promise. I'll fold every line."

She folded back and forth, back and forth, quick as a fan. Soon she held a stiff little stick of paper. There was no shape. There was no secret.

"Just guessing makes a mess of good paper," said Mark. "Read the drawing before your hands move. Look. Only some of the lines are dashed."

Lan looked at the stick in her hand.

"I said I'd do it before I checked," she said. "Sorry, Rosa."

Mark leaned over the young man's open notebook. The young man did not look up. He did not explain.

The page showed the same strip of ten triangles. There was a dashed line after the third triangle. There was another after the sixth. Before the last triangle, the line was dashes and dots.

"Every line on the drawing has a job," said Mark. "Dashes mean fold toward you. Dashes and dots mean fold away, behind. So we fold twice toward us, and the last triangle goes behind."

Rosa took a fresh strip and smoothed it flat.

"Corners first, always," said Cornelia. "Count three triangles. Now bring the rest over, so the edges meet exactly."

Rosa folded. The strip bent down and crossed itself.

"Three more," said Cornelia. "Point to point, then hold."

Rosa folded again. Now the paper was a hexagon, a shape with six sides, like a honeycomb cell. One triangle stuck out at the side.

"Three, three, three and one left over," said Inkling. "Ten."

"I'll do the last one," said Inkling. She folded the loose triangle over the front.

It landed on top of the hexagon. It did not touch the first triangle at all. Rosa tried to glue it, but there was nothing for the glue to hold.

"It won't open," said Rosa sadly. "It's just a flat lump."

"We can fix this one," said Crinkle. "Smooth it out and try again. The crease remembers."

Inkling opened the last fold. The crease showed where it had been. This time she folded the triangle behind, around the edge. It lay flat against the back of the very first triangle.

"It fits," said Rosa.

"Hold it still," said Presso. "Now press it flat. Run your thumbnail along every fold."

Rosa pressed each edge. Then she put a dab of glue on the loose triangle and held it against the first one.

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

They counted to thirty while the glue dried.

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

Kami showed Rosa how. Pinch two triangles together. Push the opposite corner in. Then open the middle like a flower.

The hexagon turned inside out. A face nobody had seen came to the front.

"There were nine triangles," said Inkling. "Each one has two sides. That's eighteen. And each face uses six. So there are three faces."

Rosa drew the moon on the front and the fish on the back. She hid the star on the face inside.

At the party, her little brother turned the hexagon over and over. Then he pinched, pushed and opened it. He shouted. There was the star.

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 wanted to make a secret card for Inkling. This time she read the lines before she folded a single one.

Tell the story back to someone. Why did the last triangle have to go behind?