Beto had taken the bell off his bicycle. He had it in pieces on the steps of the anvil: the dome, the little striker, the spring, three screws and a washer, laid out in a row on a clean rag.

"How does it work?" he said, to nobody in particular. "The spring pushes this, and this hits that. That makes five pieces. Six with the washer."

Danya sat down beside him with the Friday Paper. He turned it over, the way he always did, to the back.

This week From the Real World had a picture of a man in a coat of many colours, red and yellow and green, playing a pipe. Behind him came a river of rats, tumbling over each other. And behind the rats, small and far away, came a line of children.

Underneath it said:

In 1284 the town of Hamelin in Germany was full of rats. A piper in a coat of many colours played his pipe, and all the rats followed him into the river and drowned. But when the town refused to pay him, he played again, and all the children of Hamelin followed him away and were never seen again.

And beside it, on the Honest Page, in neat black capitals: TRUE.

Danya read it twice, with his finger under the words.

"How do we know?" he said.

Beto looked up from his bell. "How do we know what?"

"Any of it. The rats. The money. The children." Danya tapped the picture. "It's a fairy tale. It's in fairy-tale books. And they've marked it true."

"Why? Why would they do that?" said Beto.

"That's what I want to know."

Beto picked up the striker and turned it over in his fingers.

"How does it work, though?" he said. "How do you pipe a rat? Rats don't like music. Do they?"

Danya opened his notebook. Inside the cover the list of words had grown, one under the other, a word for each story he had checked since the apple. He looked at the empty space under the last one.

"I'll find out," he said.

Beto put the bell back together, all six pieces, in the right order. It rang once when he tightened the last screw, a clear little ting. Then he stood up.

"I'm coming too," he said.

The note was in the box as usual, under a card about a cat called Mrs Pickles who had gone missing on Wednesday.

Pied Piper. Mark it True. My nan grew up near there.

No name. Pencil first, then inked over, every letter.

Danya held it up to the window. The grey showed under the black, the way it always did.

"Same person," he said. "Six weeks now."

"Says who?" said Beto. "Lots of people use pencil."

"Who checked that? Not lots of people go over it in ink."

"You do," said Beto.

Danya opened his mouth, and then shut it again. He put the note in his notebook with the others.

"My nan grew up near there," he read again. "That's not a source. That's a nan."

"From where? A nan could be a source," said Beto. "If she was there."

"In 1284?"

"Well," said Beto. "No."

The printer looked up from the press.

"Back table," she said. "The big book's at Hamelin. And it's not the picture you think."

It wasn't. The big leather book lay open at a page with no rats on it at all. It was a drawing of a church window, the tall pointed kind, made of little pieces of coloured glass held together with lead. In the middle of the window stood a figure in bright colours. Around him, very small, were children dressed in white.

"No rats," said Beto.

"No rats," said Danya.

Beto leaned over the drawing until his nose almost touched it. "From where?" he said. "Where's this window? I want to see how they fit the glass together."

Danya bent over the page.

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

The spark came in under the print shop door and landed on the drawing of the window, and for a second every little piece of glass in it seemed to light up from behind. Then it went to the green curtain and waited.

The spark slid under the green curtain into the drying room, and the drying room went back much further than the shop did.

Beto went first. He always wanted to see how a place worked before anybody told him. Danya went second, holding his notebook.

The corridor was long tonight. Very long. The pages pegged up overhead stretched away into the dark like washing in a field. And from somewhere far down it, so far that it was hardly there at all, came a thin high tune, like somebody playing a pipe in another street.

Beto stopped.

"Can you hear that?"

"Yes," said Danya.

"How does it work? Where's it coming from?"

Danya shook his head. "Let's not follow it. Not yet. Not until we know what it is."

"What exactly does it say?" said a brisk voice beside them.

Claim was on her stool by the first door, with her red pencil and her pot of glue. She had a scarf wrapped twice round her neck tonight, because the corridor was cold.

Danya pointed. "Claim, this is Beto. He takes things apart."

"Good," said Claim. "So do I. Only I take sentences apart. What exactly does your paper say?"

Danya read the back page out loud. Claim listened with her head on one side.

"Say the claim in one sentence," she said.

"I can't," said Danya. "There's too much in it."

"That's the point." Claim held out her red pencil. "One claim per line."

Danya wrote them out on a clean page, leaning on the wall.

1. In 1284 Hamelin was full of rats.

2. A piper led the rats into the river.

3. The town would not pay him.

4. He led the children away, and they never came back.

5. All of it happened in 1284.

Beto counted them on his fingers. "Rats, piper, money, children, the year. That makes five."

"Five claims," said Claim. "Any of them could be true, and the others false. Fell, or hit? Those are different claims. Rats, or children? Those are different claims too."

Beto frowned. "But they're all one story."

"Are they?" said Claim. "That's what you came to find out. Underline the exact words."

Danya underlined rats in the first line and children in the fourth.

Beto frowned at the page. "The window had children. It didn't have rats."

Claim went back to her glue. "Then don't forget that. Now go and see the doors."

The first doors were the newest. A cartoon on a big screen, with a jolly piper and rats in waistcoats doing a dance. A toy theatre with cardboard rats on sticks. A poster for a town festival with a smiling piper on it. A children's book with the rats drawn so sweetly that Beto said, "I'd follow those."

Then, between two doors, there was a long wall covered in pinned-up papers and pictures, like a noticeboard in a school corridor. At the top, in big letters, somebody had written: WHAT REALLY HAPPENED?

Underneath were the guesses. Danya read them out.

They died of an illness.

They were lost in a landslide or a river.

They went to join a march far away.

They were young people, not little children, and they left to start new villages far to the east, where there was land to farm.

Beto read the last one three times. Then he turned round, and his face had gone bright.

"That one," he said. "That's it. They didn't vanish. They moved. They went to make new villages. That's a happy ending." He pointed at Danya's notebook. "Mark that one true. Then it isn't sad."

Danya hesitated. He wanted it too. A story where the children were fine was much better than a story where they were gone.

"That's an opinion. What's the claim?" said Claim.

She had come up behind them without either of them hearing, with her red pencil behind her ear.

"Why? It's not an opinion," said Beto. "It's a theory. A proper one. Somebody wrote it down."

"That's an opinion too. Somebody wrote all of them down," said Claim. "Every one on this wall is a guess about the same thing. What exactly does the wall say at the top?"

Beto looked. "What really happened."

"And does the wall know?"

Beto was quiet for a moment. "No," he said. "That's why there are lots."

"Underline the exact words," said Claim, more gently. "You can like one guess best. Lots of people like that one best. There's even something real behind it: people from that part of the country did go east, to settle. But liking a guess doesn't make it the record. Nobody knows is allowed. Write that down instead."

Beto looked at the happy guess for a long time.

"I just wanted it not to be sad," he said.

"I know," said Claim. "Most people do. That's one of the ways stories stretch."

Danya wrote Nobody knows in pencil, very small, next to his fourth claim.

They walked on. Trace was waiting at a door further along, with his notebook in his cardigan pocket.

"Where did they get it from?" he said. "Come on. The rats are this way."

The first door he showed them was a poem, printed in a handsome old book, with a picture of a piper in a long coat. The card said 1842.

"Robert Browning," said Trace. "A poet. This is the one with all the rats. Big ones, small ones, fighting the dogs, biting the babies. And a boy left behind, who couldn't keep up."

"Show me the source. Where did he get it from?" said Danya.

"Keep going back," said Trace.

The next door said 1816. Inside was a book of German stories collected by two brothers, Jacob and Wilhelm Grimm.

"The Brothers Grimm," said Beto. "The fairy-tale people."

"They collected stories," said Trace. "From old books, and from people. They didn't write this one. They wrote it down."

1842 take away 1816. "Twenty-six years before the poem," said Danya.

"A copy is not a source," said Trace. "Keep going back."

They went back a long way. The doors were further apart now. The pictures got older and stiffer, and the writing harder to read.

At a door with a card that said about 1559, Trace stopped.

Inside was a big handwritten chronicle, the kind a family keeps of its own history, with brown ink and curly letters. The card beside it said: The chronicle of Froben Christoph von Zimmern.

"Who wrote it down first?" said Trace. "With the rats, I mean. This is the earliest one we have. Before this, nobody puts rats in it at all."

Danya did the sum. 1559 take away 1284.

"Two hundred and seventy-five years," he said. "The rats turn up two hundred and seventy-five years later."

Beto had his nose almost on the glass of the case.

"So where did he get the rats from?"

"Nobody's sure," said Trace. "Some people think the rats got joined on from a different story. There are lots of stories about rat-catchers. Older isn't the same as first. Check the date. The rats are old. But the rats are not as old as the children."

"Who was there?" said a slow voice.

Weigh was coming down the corridor towards them, with his lamp in one paw and his long blue scarf trailing.

"That's not fair. Nobody here was there," said Danya. "That's the problem."

"Then let's see who was nearest," said Weigh. "Further back."

The next door was older still. The card said about 1440 to 1450. Inside was a small book written by hand in Latin, with a translation on a card beside it in plain English.

Danya read it out slowly.

It said that in the year 1284, on the feast day of Saints John and Paul, a young man of thirty, handsome and well dressed, so that everyone who saw him admired him, crossed the bridges and came into the town by the West Gate. He played a silver pipe through the streets. All the children who heard it, a hundred and thirty of them, followed him out of the East Gate to a place called Calvary, and there they vanished.

Danya stopped reading. The corridor was very quiet. Even the thin tune had stopped.

"No rats," said Beto, at last.

"No rats," said Danya. "No money. No river. Just a stranger, and the bridges, and the children."

"How long after did they say it?" said Weigh.

Danya did the sum. 1440 take away 1284. "A hundred and fifty-six years. At least. Maybe more."

"Who was there?" said Weigh.

"Not the writer," said Danya. "Nobody alive. Their great-great-grandchildren, maybe."

"Weigh it. Don't count it," said Weigh. "A long way off. But no rats. Keep that in your head."

There was one more door, very small and very plain. The card said 1384.

"This one's strange," said Trace. "We haven't got it. Not the real page. People who wrote about Hamelin's old town records say there was a line in them from 1384. Just one line."

"What did it say?"

Trace read it from his notebook. "It is a hundred years since our children left."

1384 take away 1284. "A hundred years exactly," said Danya.

"How long after did they say it? A town counting the years," said Weigh, very quietly. "That's what it sounds like. Who was there? Not the writer of that line either. But a hundred years is nearer than a hundred and fifty. A good witness can still be a long way off."

"Says who? We only know the line because other people say they saw it," said Danya.

"Weigh that too," said Weigh.

There was one door left, right at the very back of the corridor.

The card said about 1300.

The room behind it was empty. There was nothing on the walls and nothing on the stand. There was just a tall, pointed, empty frame, where a window had been.

"It's the window," said Beto. "From the big book. Where is it?"

"Gone," said Trace. "It was in a church in Hamelin. It was destroyed in 1660."

1660 take away 1300. "How do we know? It was there for three hundred and sixty years," said Danya. "And then it wasn't."

"From where, then? How do we know what was in it?" said Beto.

"People saw it," said Trace. "Before it went. And they wrote down what they saw. A piper in bright colours. Children dressed in white."

"Show me the source, then. The oldest telling is at the back," said Danya, "and it's a window, and it's gone, and all we've got is people saying what was in it."

"Weigh it. That's often how it is at the very back," said Weigh. "The oldest thing can be missing. You keep the descriptions, and you weigh them."

Beto stood in the empty room, looking up at the frame.

"How does it work, a window like that?" he said quietly. "Little bits of glass, and lead between them. Somebody made it on purpose. A long time ago, when people still remembered."

"How do we know why they made a window about it?" said Danya.

"Why? Why do you make a window about anything?" said Beto. "So you don't forget."

They sat down on the floor of the corridor, under the pegged-up pages. Danya looked at his five claims.

1. In 1284 Hamelin was full of rats.

No. Nobody mentions rats until about 1559.

2. A piper led the rats into the river.

Not in the oldest tellings.

3. The town would not pay him.

Not in the oldest tellings either. That came with the rats.

4. He led the children away, and they never came back.

The window, the 1384 line, the Lüneburg book. All of them have the children. Nobody knows what happened to them.

5. All of it happened in 1284.

The children part, the old tellings say so. The rats part, nobody says so for two hundred and seventy-five years.

"I could take it apart," said Beto suddenly. He had been quiet a long time. "The story. Like the bell."

"Go on."

"I could take it apart. There are two pieces," said Beto. He held up one hand. "This piece is old. A stranger comes over the bridges. The children follow him. They don't come back. The town is so sad it makes a window and counts the years." He held up the other hand. "This piece is newer. Rats. A bill nobody pays. A piper who gets cross."

"Who checked that? Somebody stuck them together," said Danya.

"Why?" said Beto. "I think it's because the old piece doesn't have a reason in it. Children just go. That's too sad and too strange. So somebody added the rats and the money, and then it has a reason. He took them because they didn't pay. Then it's a story with a lesson."

"Keep your promises," said Danya.

"Yes," said Beto. "That's what they teach with it now. But that's the new piece. The old piece doesn't teach anything. It just remembers."

"Who was there? Nobody who's alive. Weigh it," said Weigh, who had sat down with them, with a great deal of care. "But the people who made the window were nearer than anyone. Weigh them first."

"Were the people who added the rats lying?" said Danya.

"Did they think it was true?" said Weigh.

"Maybe."

"Then they weren't lying. Weigh it. People like a better story," said Weigh. "A story with a reason is easier to tell than a story with a hole in it."

"Stretching is honest," said Trace, "when you say that you did it."

Danya wrote the correction.

From the Real World — a correction.

In 1284, 130 children followed a stranger with a pipe out of the town of Hamelin and did not come back. TRUE that the town remembered it. A church window of about 1300, an entry in the town's records from 1384, and a book written about 1440 to 1450 all tell of the children.

What happened to the children. NOBODY KNOWS. Historians have many ideas. None is agreed.

The piper rid the town of rats, and the town would not pay him. STRETCHED. The oldest tellings have no rats and no money. The rats first appear about 1559, two hundred and seventy-five years later.

At the bottom, in pencil, he added a line: Ask someone who knows a story from where they grew up. Is there an old piece and a new piece? Then he inked over the pencil, the way he always did now, so the printer could read it. He did not stop to look at it.

He showed it to Claim. She underlined remembered and nobody knows and nodded.

He showed it to Trace. Trace checked every date, and said, "Two hundred and seventy-five. That's right. Keep going back."

He showed it to Weigh.

"Weighed," said the old bear. "Not counted. And you left the sad part in."

"That's not fair. I didn't want to," said Danya.

"Nor did I," said Beto.

Inside the cover of his notebook, under the other words, Danya wrote one more: RATS. Then he looked at it, and drew a little line through it, and wrote beside it, very small: added later.

The spark slid back under the curtain, and the drying room was just a cupboard again.

The big book on the back table was still open at the drawing of the window. The children in white stood around the piper, small and still.

The printer read the correction all the way through, twice.

"That goes in as it is," she said. "Sad part and all."

"And the note?" said Beto. "The nan one?"

"Still no name," said the printer. "But if somebody's nan grew up near Hamelin, she'd know there's more than one way to tell it. Every town has a story like that."

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

Back on the Green

Tí found Beto by the anvil the next afternoon, with the bicycle bell in pieces again.

"Again!" said Tí. "Tell me the rat one again."

"Why? The rat one is only half of it," said Beto. He laid the pieces out on the rag. "Look. This is the old half." He pushed the dome to one side. "And this is the new half." He pushed the spring and the striker to the other.

Tí looked at the two piles. "Which half has the rats?"

"The new half."

"And the music?"

"Both halves," said Beto. "There's always a piper."

Danya sat down beside them.

"In Hamelin," he said, "there's a street called the street without drums. The town says that's the way the children went. Nobody plays music there. Not even now. Not even at a festival."

Tí thought about that for a while. Then he picked up the dome of the bell and held it very carefully, so it didn't ring.

"So it stays quiet," he said.

"So it stays quiet. That makes six pieces, and none of them rings," said Beto. "So nobody forgets."

Tí held the dome for a long moment. Then he gave it back, and Beto put the bell together, all six pieces, in the right order, and this time he didn't ring it either.

Then Tí ran off across the Green after a butterfly, and Lan ran after him, and the afternoon was ordinary again.