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.