They walked for fully half an hour, the wall unbroken. There were places where cracks had appeared in it - though none low enough to offer hand-holds - and others where the top edge showed signs of crumbling, but there was neither window nor gate in its length, however small.

'Who built this?' said Hobart as they walked.

Shadwell was watching their shadow on the wall, as it kept pace with them.

'Ancients,' he said.

To keep the desert out?'

'Or keep the Scourge in.'

The last few minutes had brought a subtle change in the wind. It had given up nipping at their legs, and gone about braver business. It was Ibn Talaq who first spotted what.

'There! There!' he said, and pointed along the wall.

A few hundred yards from where they stood a stream of sand was being carried out through the wall, bellowing as it went. As they approached, it became apparent that this was not a gate, but a breach in the wall. The stone had been thrown down in heaps of rubble. Shadwell was first to reach the scattered pieces, many the size of small houses, and began to scramble up over them, until at last he looked down into the place the walls had been raised to guard.

Behind him, Hobart called: 'What do you see?'

Shadwell didn't speak. He simply surveyed the scene behind the wall with disbelieving eyes, as the wind that roared through the breach threatened to throw him from his perch.

There were neither palaces nor tombs on the other side of the wall. Indeed there was no sign, however vestigial, of habitation; no obelisks, no colonnades. There was only sand, and more sand; endless sand. Another desert, rolling away from them, as empty as the void at their backs.

'Nothing.'

It wasn't Shadwell who spoke but Hobart. He too had scaled the boulders, and stood at Shadwell's side.

'Oh Jesus ... nothing.'

Shadwell made no reply. He simply clambered down the other side of the breach, and stepped into the shadow of the wall. What Hobart said appeared to be true: there was nothing here. Why then did he feel certain that this place was somehow sacred?

He walked through the mire of sand that the wind had heaped against the rubble of the breach, and surveyed the dunes. Was it possible that the sand had simply covered the secret they'd come here to find? Was the Scourge concealed here, its howl that of something buried alive? If so, how could they ever hope to locate it?

He turned back, and squinted up at the wall. Then, on impulse, he began to climb the open edge of the breach. It was heavy going. His limbs were weary, and the wind had polished the stone in its many years of passage, but he eventually gained the summit.

At first it seemed his efforts had been for nothing. All he'd won for his sweat was a view of the wall, running off in both directions until distance claimed it.

But when he came to survey the scene below, he realized that there was a pattern visible in the dunes. Not the natural wave patterns that the wind created, but something more elaborate - vast geometrical designs laid out in the sand - with walkways or roads between them. He'd read, in his research on wastelands, of designs drawn by some ancient people on the plains of South America; pictures of birds and gods that could have made no sense from the earth, but had been drawn as if to enchant some heavenly spectator. Was that the case here? Had the sand been raised in these furrows and banks as a message to the sky? If so, what power had done it? A small nation would be needed to move so much sand; and the wind would undo tomorrow what had been done today. Whose work was this then?

Perhaps night would tell.

He climbed back down the wall to where Hobart and the others were waiting amid the boulders.

'We'll camp here tonight,' he said.

'Inside the walls or out?' Hobart wanted to know.

'Inside.'

IV.

URIEL.

Night came down like a dropped curtain. Jabir made a fire in the shelter of the wall, out of the remorseless assault of the wind, and there they ate bread and drank coffee. There was no conversation. Exhaustion had claimed their tongues. They simply sat hunched up, staring into the flames.

Though his bones ached, Shadwell couldn't sleep. As the fire burned low, and one by one the others succumbed to fatigue, he was left to keep watch. The wind dropped a little as the night deepened, its bellow becoming a moan. It soothed him like a lullaby, and at last, his eyelids dropped closed. Behind them, the busy patterns of his inner-eye. Then emptiness.

In sleep, he heard the boy Jabir's voice. It called him from darkness but he didn't want to answer. Rest was too sweet. It came again, however: a horrid shriek. This time he opened his lids.

The wind had died completely. Overhead the stars were bright in a perfect sky, trembling in their places. The fire had gone out, but their light was sufficient for him to see that both Ibn Talaq and Jabir were missing from their places. He got up, crossed to Hobart, and shook him awake.

As he did so, his eye caught sight of something on the ground a little way beyond Hobart's head. He stared - doubting what he saw.

There were flowers underfoot, or so he seemed to see. Clusters of blooms, set in abundant foliage. He looked up from the ground, and his parched throat unleashed a cry of astonishment.

The dunes had gone. In their place a jungle had risen up, a riot of trees that challenged the wall's height - vast, flower-laden species whose leaves were the size of a man. Beneath their canopy was a wilderness of vines and shrubs and grasses.

For a moment he doubted his sanity, until he heard Hobart say: 'My God,' at his side.

'You see it too?' said Shadwell.

'I see it...' Hobart said,'... a garden.'

'Garden?'

At first sight the word scarcely described this chaos. But further scrutiny showed that there was order at work in what had initially seemed anarchy. Avenues had been laid under the vast, blossom-laden trees; there were lawns and terraces. This was indeed a garden of sorts, though there would be little pleasure to be had walking in it, for despite the surfeit of species - plants and bushes of every size and shape - there was not amongst them a single variety that had colour. Neither bloom nor branch nor leaf nor fruit; all, down to the humblest blade, had been bled of pigment.

Shadwell was puzzling at this when a further cry issued from the depths. It was Ibn Talaq's voice this time; and it rose in a steep curve to a shriek. He followed it. The ground was soft beneath his feet, which slowed his progress, but the shriek went on, broken only by sobbing breaths. Shadwell ran, calling the man's name. There was no fear left in him; only an overwhelming hunger to see the Maker of this enigma face to face.

As he advanced down one of the shadowy boulevards, its pathway strewn with the same colourless plant-life, Ibn Talaq's cry stopped dead. Shadwell was momentarily disoriented. He halted, and scanned the foliage for some sign of movement. There was none. The breeze did not stir a single frond; nor - to further compound the mystery - was there a hint of perfume, however subtle, from the mass of blossoms.

Behind him, Hobart muttered a cautionary word. Shadwell turned, and was about to condemn the man's lack of curiosity when he caught sight of the trail his own footsteps had made. In the Gyre, his heels had brought forth life. Here, they'd destroyed it. Wherever he'd set foot the plants had simply crumbled away.

He stared at the blank ground where there'd previously been grasses and flowers, and the explanation for this extraordinary growth became apparent. Ignoring Hobart now, he walked towards the nearest of the bushes, the blooms of which hung like censers from their branches. Tentatively, he touched his fingers to one of the flowers. Upon this lightest of contacts the blossom fell apart, dropping from the branch in a shower of sand. He brushed its companion with his thumb: it too fell away, and with it the branch, and the exquisite leaves it bore; all returned to sand at a touch.

The dunes hadn't disappeared in the night, to make way for this garden. They had become the garden; risen up at some unthinkable command to create this sterile illusion. What had at first sight seemed a miracle of fecundity was a mockery. It was sand. Scentless, colourless, lifeless: a dead garden.

A sudden disgust gripped him. This trick was all too like the work of the Seerkind: some deceitful rapture. He flung himself into the midst of the shrubbery, flailing to right and left of him in his fury, destroying the bushes in stinging clouds. A tree, brushed by his hand, collapsed like an extinguished fountain. The most elaborate blossoms fell apart at his merest touch. But he wasn't satisfied. He flailed on until he'd cleared a small grove amid the press of foliage.

'Raptures!' he kept yelling, as the sand rained down on him. 'Raptures!'

He might have gone on to more ambitious destruction, but that the Scourge's howl - the same he'd first heard days before, as he'd squatted in shit - began. That voice had brought him through desolation and emptiness; and to what? More desolation, more emptiness. His anger unassuaged by the damage he'd done, he turned to Hobart.

'Which way's it coming from?'

'I don't know,' said Hobart, stumbling back a few steps. 'Everywhere.'