Later, when his mother had gone out to work and ould Kasim was back on his stool, watching boys scrap and small girls hurry home with wild snails for that evening's soup, Moz clambered over the edge of the roof, dropped onto a pile of crates stacked against the side of their house and jumped from here to the ground. All this he did one-handed.

Most of his magazine was gone, used to set a fire in the grate of ould Kasim's kitchen, but what little was left Moz took to a bench in the Jardin Aguedal, working meaning from the letters by the light of a dying sun.

From where he sat, Moz could see a stork's nest set like a turret on the city walls. The comforting smell of warm dung rose from two donkeys tethered under a tree behind him. There were other smells warming the air, charcoal from a bread oven and grilled meat, goat probably. He could almost taste the greasy smoke as it drifted from a house on the other side of the gate.

And then Moz put his hunger aside and turned to the scraps of magazine. There was a wall in China so big it could be seen from space. This wall was in urgent need of repair. Solid objects were not really solid but made from vibrations. Clever people believed more worlds than one might exist. And one day machines might be smarter than humans (although the person writing said this was unlikely).

Even after he'd laboriously spelt words out one letter at a time, saying them aloud to the darkening sky, many remained hard, but their meaning could sometimes be guessed from simpler words on either side.

And so the parasite entered his brain and changed everything. It changed how Moz saw life now that he knew nothing was as it seemed and the wall on which the storks nested, his roof and the scraps of torn magazine in his hand were made of spaces between vibrations which moved around each other, attracting and repelling.

This knowledge ate out the certainties of his life and kept eating until it changed the way things felt beneath his hand. Somehow everything in the Mellah became less solid and more ghostlike than it had been before.

He talked to a Sufi at the mosque near Dar si Said, where Rue Zitoun el Jedid met an alley that cut through to Rue Zitoun el Kedim. It was a small mosque and not as important as La Koutoubia or the mosque in Quartier Berima, which was nearer but also opposite the Royal Palace.

The Sufi was one of a circle of old men who sat cross-legged on a bench outside, talking quietly among themselves. It took Moz three weeks to summon the courage to approach the man because Hajj Rahman was the oldest and wisest of those who met each day.

Like Marrakech's famous red walls, La Koutoubia and many of the city's older buildings, the sides of the little mosque were pocked with square holes left by wooden scaffolding from when it was built many years before. The city's pigeons and doves had been squatting in them ever since.

"Please..." Moz said.

The Sufi looked up to see a small boy with an empty sleeve pinned crudely to the front of his jellaba. "What is it?" he demanded.

The one-armed boy shuffled his feet and tugged at the neck of a threadbare gown. He had flour on his fingers and a chunk of bread bulged from his pocket, neither of which was appropriate for the place in which he found himself. In between shuffling his feet and glancing at the Sufi, the boy seemed to be matching pigeons to their holes in the wall.

"Are you in trouble?" Boys were sent to him for punishment, mostly by mothers who believed he could change things he could not. "Well?" demanded the Sufi.

"No more than usual..."

Hajj Rahman smiled, examining the boy properly for the first time. His hair was dark blond, which was not unusual in the Atlas. He had the sallow skin of a Berber and cheekbones to match, but his eyes were almost black. The Sufi could not remember having seen him before.

"What's your name?"

"Turq."

The old man shook his head. "Your name," he said, "not where your father comes from."

"That's what people call me," the boy answered, his voice apologetic.

"And your father," the Sufi asked, "does he call you Turk?"

"No," said Moz, "he left."

"Your mother then." For a second the man looked thoughtful. "You do have a mother?"

Moz nodded. "She calls me Moz."

"Short for what?"

"I don't know," said the boy. "She's German," he added, as if one might explain the other.

"And your father was Turkish." Hajj Rahman nodded to himself as everything fell into place. He knew of this boy, whose mother sold majoun, cakes of marijuana, to foreigners on Djemaa el Fna and sometimes went to their beds.

"Tell me why you're here," said the Sufi, but Moz just stood there. A couple of times his mouth opened and then he dropped his eyes and turned away.

"I said, tell me."

"It was a stupid question," said Moz. "I'm sorry."

"Let me be the judge," ordered the Sufi.

There are some who believe there are no stupid or unnecessary questions. Hajj Rahman was not one of those. Almost every major question which could be asked had already been answered, either in the Holy Qur'an or the Hadith, the sayings and case law of Islamic wisdom or by the Sufi masters.

"I've been trying to find out about things."

"Ah," said the man, "I see..." Tugging at his beard, Hajj Rahman adjusted his jellaba until he could sit more comfortably. "What things?"

The Sufi treated the boy's question with great dignity. A far greater dignity than he would have shown to someone twice the boy's age.

Moz gestured to the crowded street and to those wheeling carts or riding past on tiny motorbikes or dodging this traffic, then he included himself and the old man with the white beard.

"Ah." Hajj Rahman smiled. "You wish to know about God."

"No," said Moz, as politely as he could. "Mostly I want to know about atoms and how long a mile is."

"Whatever they are," said Hajj Rahman, "the one made the other." At the sight of the boy's puzzled frown, the old man gestured that Moz should join him on the bench.

This the boy did, awkwardly.

"There are ninety-nine names of God," explained the Sufi. "The Merciful, the Subtle, the Apparent... These are written. Without knowing it, we all search for the Hundredth Name."

Moz didn't mean to be rude. He was just too surprised to remember to be polite, even to a hajj. "Says who?" he asked.

"It's agreed," said the Sufi. "And everyone is looking, including you."

Glancing at the boy, he saw matted hair and broken nails, fingers grimed with dirt and flour and an oversized jellaba that was filthier still. And then he looked beneath this and saw hunger, of a kind not fed by food.

"This word," said Moz.

"Which one?"

"The name."

"Who said it was a word?" Hajj Rahman asked.

"You did."

"No," said the Sufi. "That's not what I said at all. It could be a sunset or a perfect number. A pattern of tiles so beautiful that suicides decide to live. Not having found it, how can anyone know what this name might be?"

"It could be a number?"

"Of course," said the Sufi. "It could also be a perfect note, a falling leaf. There are seventy-two paths open to humanity." He gestured to the mosque beside them. "Beauty is only one of them... You know what writing is?"

Moz scowled. Of course he knew.

"Everything is written," said the Sufi.

If all things were written, then... "I don't understand," said Moz, "everything is decided in advance?"

"No." The Sufi shook his head. "Everything is written. All paths and all possibilities, but you should not worry yourself about this." He smiled at the boy, face thoughtful. "In fact," he said, "many people do not worry about such things at all."

It was only after Moz had thanked the Sufi and left that he realized he still didn't know the length of a mile.