"Yeah," said the red-haired girl, in the garden of the deserted casino. "We seen her, me and Paolo both seen her. She come through here days ago."

Father Gomez said, "And do you remember what she looked like?"

"She look hot," said the little boy. "Sweaty in the face, all right."

"How old did she seem to be?"

"About..." said the girl, considering, "I suppose maybe forty or fifty. We didn't see her close. She could be thirty, maybe. But she was hot, like Paolo said, and she was carrying a big rucksack, much bigger than yours, this big..."

Paolo whispered something to her, screwing up his eyes to look at the priest as he did so. The sun was bright in his face.

"Yeah," said the girl impatiently, "I know. The Specters," she said to Father Gomez, "she wasn' afraid of the Specters at all. She just walked through the city and never worried a bit. I ain' never seen a grownup do that before, all right. She looked like she didn' know about them, even. Same as you," she added, looking at him with a challenge in her eyes.

"There's a lot I don't know," said Father Gomez mildly.

The little boy plucked at her sleeve and whispered again.

"Paolo says," she told the priest, "he thinks you're going to get the knife back."

Father Gomez felt his skin bristle. He remembered the testimony of Fra Pavel in the inquiry at the Consistorial Court: this must be the knife he meant.

"If I can," he said, "I shall. The knife comes from here, does it?"

"From the Torre degli Angeli," said the girl, pointing at the square stone tower over the red-brown rooftops. It shimmered in the midday glare. "And the boy who stole it, he kill our brother, Tullio. The Specters got him, all right. You want to kill that boy, that's okay. And the girl - she was a liar, she was as bad as him."

"There was a girl, too?" said the priest, trying not to seem too interested.

"Lying filth," spat the red-haired child. "We nearly killed them both, but then there came some women, flying women - "

"Witches," said Paolo.

"Witches, and we couldn' fight them. They took them away, the girl and boy. We don' know where they went. But the woman, she came later. We thought maybe she got some kind of knife, to keep the Specters away, all right. And maybe you have, too," she added, lifting her chin to stare at him boldly.

"I have no knife," said Father Gomez. "But I have a sacred task. Maybe that is protecting me against these - Specters."

"Yeah," said the girl, "maybe. Anyway, you want her, she went south, toward the mountains. We don' know where. But you ask anyone, they know if she go past, because there ain' no one like her in Ci'gazze, not before and not now. She be easy to find."

"Thank you, Angelica," said the priest. "Bless you, my children."

He shouldered his pack, left the garden, and set off through the hot, silent streets, satisfied.

After three days in the company of the wheeled creatures, Mary Malone knew rather more about them, and they knew a great deal about her.

That first morning they carried her for an hour or so along the basalt highway to a settlement by a river, and the journey was uncomfortable; she had nothing to hold on to, and the creature's back was hard. They sped along at a pace that frightened her, but the thunder of their wheels on the hard road and the beat of their scudding feet made her exhilarated enough to ignore the discomfort.

And in the course of the ride she became more aware of the creatures' physiology. Like the grazers' skeletons, theirs had a diamond-shaped frame, with a limb at each of the corners. Sometime in the distant past, a line of ancestral creatures must have developed this structure and found it worked, just as generations of long-ago crawling things in Mary's world had developed the central spine.

The basalt highway led gradually downward, and after a while the slope increased, so the creatures could freewheel. They tucked their side legs up and steered by leaning to one side or the other, and hurtled along at a speed Mary found terrifying - though she had to admit that the creature she was riding never gave her the slightest feeling of danger. If only she'd had something to hold on to, she would have enjoyed it.

At the foot of the mile-long slope, there was a stand of the great trees, and nearby a river meandered on the level grassy ground. Some way off, Mary saw a gleam that looked like a wider expanse of water, but she didn't spend long looking at that, because the creatures were making for a settlement on the riverbank, and she was burning with curiosity to see it.

There were twenty or thirty huts, roughly grouped in a circle, made of - she had to shade her eyes against the sun to see - wooden beams covered with a kind of wattle-and-daub mixture on the walls and thatch on the roofs. Other wheeled creatures were working: some repairing a roof, others hauling a net out of the river, others bringing brushwood for a fire.

So they had language, and they had fire, and they had society. And about then she found an adjustment being made in her mind, as the word creatures became the word people. These beings weren't human, but they were people, she told herself; it's not them, they're us.

They were quite close now, and seeing what was coming, some of the villagers looked up and called to each other to look. The party from the road slowed to a halt, and Mary clambered stiffly down, knowing that she would ache later on.

"Thank you," she said to her, her what? Her steed? Her cycle? Both ideas were absurdly wrong for the bright-eyed amiability that stood beside her. She settled for - friend.

He raised his trunk and imitated her words:

"Anku," he said, and again they laughed, in high spirits.

She took her rucksack from the other creature ("Anku! Anku!") and walked with them off the basalt and on to the hard-packed earth of the village.

And then her absorption truly began.

In the next few days she learned so much that she felt like a child again, bewildered by school. What was more, the wheeled people seemed to be just as wonderstruck by her. Her hands, to begin with. They couldn't get enough of them: their delicate trunks felt over every joint, searching out thumbs, knuckles, and fingernails, flexing them gently, and they watched with amazement as she picked up her rucksack, conveyed food to her mouth, scratched, combed her hair, washed. In return, they let her feel their trunks. They were infinitely flexible, and about as long as her arm, thicker where they joined the head, and quite powerful enough to crush her skull, she guessed. The two finger-like projections at the tip were capable of enormous force and great gentleness; the creatures seemed to be able to vary the tone of their skin on the underside, on their equivalent of fingertips, from a soft velvet to a solidity like wood. As a result, they could use them for both a delicate task like milking a grazer and the rough business of tearing and shaping branches.

Little by little, Mary realized that their trunks were playing a part in communication, too. A movement of the trunk would modify the meaning of a sound, so the word that sounded like "chuh" meant water when it was accompanied by a sweep of the trunk from left to right, rain when the trunk curled up at the tip, sadness when it curled under, and young shoots of grass when it made a quick flick to the left. As soon as she saw this, Mary imitated it, moving her arm as best she could in the same way, and when the creatures realized that she was beginning to talk to them, their delight was radiant.

Once they had begun to talk (mostly in the wheeled people's language, although she managed to teach them a few words of English: they could say "anku" and "grass" and "tree" and "sky" and "river," and pronounce her name, with a little difficulty) they progressed much more quickly. Their word for themselves as a people was mulefa, but an individual was a zalif. Mary thought there was a difference between the sounds for he-zalif and she-zalif, but it was too subtle for her to imitate easily. She began to write it all down and compile a dictionary.

But before she let herself become truly absorbed, she took out her battered paperback and the yarrow stalks, and asked the I Ching: Should I be here doing this, or should I go on somewhere else and keep searching?

The reply came: Keeping still, so that restlessness dissolves; then, beyond the tumult, one can perceive the great laws.

It went on: As a mountain keeps still within itself, thus a wise man does not permit his will to stray beyond his situation.

That could hardly be clearer. She folded the stalks away and closed the book, and then realized that she'd drawn a circle of watching creatures around her.

One said, Question? Permission? Curious.

She said, Please. Look.

Very delicately their trunks moved, sorting through the stalks in the same counting movement she'd been making, or turning the pages of the book. One thing they were astonished by was the doubleness of her hands: by the fact that she could both hold the book and turn the pages at the same time. They loved to watch her lace her fingers together, or play the childhood game of "This is the church, and this is the steeple," or make that over-and-over thumb-to-opposite forefinger movement that was what Ama was using, at exactly the same moment in Lyra's world, as a charm to keep evil spirits away.

Once they had examined the yarrow stalks and the book, they folded the cloth over them carefully and put them with the book into her rucksack. She was happy and reassured by the message from ancient China, because it meant that what she wanted most to do was exactly, at that moment, what she should do.

So she set herself to learning more about the mulefa, with a cheerful heart.

She learned that there were two sexes, and that they lived monogamously in couples. Their offspring had long childhoods - ten years at least - growing very slowly, as far as she could interpret their explanation. There were five young ones in this settlement, one almost grown and the others somewhere in between, and being smaller than the adults, they could not manage the seedpod wheels. The children had to move as the grazers did, with all four feet on the ground, but for all their energy and adventurousness (skipping up to Mary and shying away, trying to clamber up tree trunks, floundering in the shallow water, and so on), they seemed clumsy, as if they were in the wrong element. The speed and power and grace of the adults was startling by contrast, and Mary saw how much a growing youngster must long for the day when the wheels would fit. She watched the oldest child, one day, go quietly to the storehouse where a number of seedpods were kept, and try to fit his foreclaw into the central hole; but when he tried to stand up, he fell over at once, trapping himself, and the sound attracted an adult. The child struggled to get free, squeaking with anxiety, and Mary couldn't help laughing at the sight, at the indignant parent and the guilty child, who pulled himself out at the last minute and scampered away.

The seedpod wheels were clearly of the utmost importance, and soon Mary began to see just how valuable they were.

The mulefa spent much of their time, to begin with, in maintaining their wheels. By deftly lifting and twisting the claw, they could slip it out of the hole, and then they used their trunks to examine the wheel all over, cleaning the rim, checking for cracks. The claw was formidably strong: a spur of horn or bone at right angles to the leg, and slightly curved so that the highest part, in the middle, bore the weight as it rested on the inside of the hole. Mary watched one day as a zalif examined the hole in her front wheel, touching here and there, lifting her trunk up in the air and back again, as if sampling the scent.

Mary remembered the oil she'd found on her fingers when she had examined the first seedpod. With the zalif 's permission she looked at her claw, and found the surface more smooth and slick than anything she'd felt on her world. Her fingers simply would not stay on the surface. The whole of the claw seemed impregnated with the faintly fragrant oil, and after she had seen a number of the villagers sampling, testing, checking the state of their wheels and their claws, she began to wonder which had come first: wheel or claw? Rider or tree?

Although of course there was a third element as well, and that was geology. Creatures could only use wheels on a world that provided them with natural highways. There must be some feature of the mineral content of these stone roads that made them run in ribbon-like lines over the vast savanna, and be so resistant to weathering or cracking. Little by little, Mary came to see the way everything was linked together, and all of it, seemingly, managed by the mulefa. They knew the location of every herd of grazers, every stand of wheel trees, every clump of sweet grass, and they knew every individual within the herds, and every separate tree, and they discussed their well-being and their fate. On one occasion she saw the mulefa cull a herd of grazers, selecting some individuals and herding them away from the rest, to dispatch them by breaking their necks with a wrench of a powerful trunk. Nothing was wasted. Holding flakes of razor-sharp stone in their trunks, the mulefa skinned and gutted the animals within minutes, and then began a skillful butchery, separating out the offal and the tender meat and the tougher joints, trimming the fat, removing the horns and the hooves, and working so efficiently that Mary watched with the pleasure she felt at seeing anything done well.

Soon strips of meat were hanging to dry in the sun, and others were packed in salt and wrapped in leaves; the skins were scraped clear of fat, which was set by for later use, and then laid to soak in pits of water filled with oak bark to tan; and the oldest child was playing with a set of horns, pretending to be a grazer, making the other children laugh. That evening there was fresh meat to eat, and Mary feasted well.

In a similar way the mulefa knew where the best fish were to be had, and exactly when and where to lay their nets. Looking for something she could do, Mary went to the net-makers and offered to help. When she saw how they worked, not on their own but two by two, working their trunks together to tie a knot, she realized why they'd been so astonished by her hands, because of course she could tie knots on her own. At first she felt that this gave her an advantage - she needed no one else - and then she realized how it cut her off from others. Perhaps all human beings were like that. And from that time on, she used one hand to knot the fibers, sharing the task with a female zalif who had become her particular friend, fingers and trunk moving in and out together.

But of all the living things the wheeled people managed, it was the seedpod trees that they took most care with.

There were half a dozen groves within the area looked after by this group. There were others farther away, but they were the responsibility of other groups. Each day a party went out to check on the well-being of the mighty trees, and to harvest any fallen seedpods. It was clear what the mulefa gained; but how did the trees benefit from this interchange? One day she saw. As she was riding along with the group, suddenly there was a loud crack, and everyone came to a halt, surrounding one individual whose wheel had split. Every group carried a spare or two with it, so the zalif with the broken wheel was soon remounted; but the broken wheel itself was carefully wrapped in a cloth and taken back to the settlement.

There they prized it open and took out all the seeds - flat pale ovals as big as Mary's little fingernail - and examined each one carefully. They explained that the seedpods needed the constant pounding they got on the hard roads if they were to crack at all, and also that the seeds were difficult to germinate. Without the mulefa 's attention, the trees would all die.

Each species depended on the other, and furthermore, it was the oil that made it possible. It was hard to understand, but they seemed to be saying that the oil was the center of their thinking and feeling; that young ones didn't have the wisdom of their elders because they couldn't use the wheels, and thus could absorb no oil through their claws.

And that was when Mary began to see the connection between the mulefa and the question that had occupied the past few years of her life.

But before she could examine it any further (and conversations with the mulefa were long and complex, because they loved qualifying and explaining and illustrating their arguments with dozens of examples, as if they had forgotten nothing and everything they had ever known was available immediately for reference), the settlement was attacked.

Mary was the first to see the attackers coming, though she didn't know what they were.

It happened in midafternoon, when she was helping repair the roof of a hut. The mulefa only built one story high, because they were not climbers; but Mary was happy to clamber above the ground, and she could lay thatch and knot it in place with her two hands, once they had shown her the technique, much more quickly than they could.

So she was braced against the rafters of a house, catching the bundles of reeds thrown up to her, and enjoying the cool breeze from the water that was tempering the heat of the sun, when her eye was caught by a flash of white.

It came from that distant glitter she thought was the sea. She shaded her eyes and saw one - two - more, a fleet of tall white sails, emerging out of the heat haze, some way off but making with a silent grace for the river mouth.

Mary! called the zalif from below. What are you seeing?

She didn't know the word for sail, or boat, so she said tall, white, many.

At once the zalif gave a call of alarm, and everyone in earshot stopped work and sped to the center of the settlement, calling the young ones. Within a minute all the mulefa were ready to flee.

Atal, her friend, called: Mary! Mary! Come! Tualapi! Tualapi!

It had all happened so quickly that Mary had hardly moved. The white sails by this time had already entered the river, easily making headway against the current. Mary was impressed by the discipline of the sailors: they tacked so swiftly, the sails moving together like a flock of starlings, all changing direction simultaneously. And they were so beautiful, those snow white slender sails, bending and dipping and filling -

There were forty of them, at least, and they were coming upriver much more swiftly than she'd thought. But she saw no crew on board, and then she realized that they weren't boats at all: they were gigantic birds, and the sails were their wings, one fore and one aft, held upright and flexed and trimmed by the power of their own muscles.

There was no time to stop and study them, because they had already reached the bank, and were climbing out. They had necks like swans, and beaks as long as her forearm. Their wings were twice as tall as she was, and - she glanced back, frightened now, over her shoulder as she fled - they had powerful legs: no wonder they had moved so fast on the water.

She ran hard after the mulefa, who were calling her name as they streamed out of the settlement and onto the highway. She reached them just in time: her friend Atal was waiting, and as Mary scrambled on her back, Atal beat the road with her feet, speeding away up the slope after her companions.

The birds, who couldn't move as fast on land, soon gave up the chase and turned back to the settlement.

They tore open the food stores, snarling and growling and tossing their great cruel beaks high as they swallowed the dried meat and all the preserved fruit and grain. Everything edible was gone in under a minute.

And then the tualapi found the wheel store, and tried to smash open the great seedpods, but that was beyond them. Mary felt her friends tense with alarm all around her as they watched from the crest of the low hill and saw pod after pod hurled to the ground, kicked, rasped by the claws on the mighty legs, but of course no harm came to them from that. What worried the mulefa was that several of them were pushed and shoved and nudged toward the water, where they floated heavily downstream toward the sea.

Then the great snow-white birds set about demolishing everything they could see with brutal, raking blows of their feet and stabbing, smashing, shaking, tearing movements of their beaks. The mulefa around her were murmuring, almost crooning with sorrow.

I help, Mary said. We make again.

But the foul creatures hadn't finished yet; holding their beautiful wings high, they squatted among the devastation and voided their bowels. The smell drifted up the slope with the breeze; heaps and pools of green-black-brown-white dung lay among the broken beams, the scattered thatch. Then, their clumsy movement on land giving them a swaggering strut, the birds went back to the water and sailed away downstream toward the sea.

Only when the last white wing had vanished in the afternoon haze did the mulefa ride down the highway again. They were full of sorrow and anger, but mainly they were powerfully anxious about the seedpod store.

Out of the fifteen pods that had been there, only two were left. The rest had been pushed into the water and lost. But there was a sandbank in the next bend of the river, and Mary thought she could spot a wheel that was caught there; so to the mulefa 's surprise and alarm, she took off her clothes, wound a length of cord around her waist, and swam across to it. On the sandbank she found not one but five of the precious wheels, and passing the cord through their softening centers, she swam heavily back, pulling them behind her.

The mulefa were full of gratitude. They never entered the water themselves, and only fished from the bank, taking care to keep their feet and wheels dry. Mary felt she had done something useful for them at last.

Later that night, after a scanty meal of sweet roots, they told her why they had been so anxious about the wheels. There had once been a time when the seedpods were plentiful, and when the world was rich and full of life, and the mulefa lived with their trees in perpetual joy. But something bad had happened many years ago - some virtue had gone out of the world - because despite every effort and all the love and attention the mulefa could give them, the wheel-pod trees were dying.