he mulefa made many kinds of rope and cord, and Mary Malone spent a morning inspecting and testing the ones Atal's family had in their stores before choosing what she wanted. The principle of twisting and winding hadn't caught on in their world, so all the cords and ropes were braided; but they were strong and flexible, and Mary soon found exactly the sort she wanted.

What are you doing? said Atal.

The mulefa had no term for climb, so Mary had to do a lot of gesturing and roundabout explaining. Atal was horrified.

To go into the high part of the trees?

I must see what is happening, Mary explained. Now you can help me prepare the rope.

Once in California, Mary had met a mathematician who spent every weekend climbing among the trees. Mary had done a little rock climbing, and she'd listened avidly as he had talked about the techniques and equipment. She had decided to try it herself as soon as she had the chance. Of course she'd never expected to be climbing trees in another universe, and climbing solo didn't greatly appeal, either, but there was no choice about that. What she could do was make it as safe as possible beforehand.

She took a coil long enough to reach over one of the branches of a high tree and back down to the ground, and strong enough to bear several times her weight. Then she cut a large number of short pieces of a smaller but very tough cord and made slings with them: short loops tied with a fisherman's knot, which could make hand¨C and footholds when she tied them to the main line.

Then there was the problem of getting the rope over the branch in the first place. An hour or two's experimenting with some fine tough cord and a length of springy branch produced a bow; the Swiss Army knife cut some arrows, with stiff leaves in place of feathers to stabilize them in flight; and finally, after a day's work, Mary was ready to begin. But the sun was setting, and her hands were tired, and she ate and slept, preoccupied, while the mulefa discussed her endlessly in their quiet, musical whispers.

First thing in the morning, she set off to shoot an arrow over a branch. Some of the mulefa gathered to watch, anxious for her safety. Climbing was so alien to creatures with wheels that the very thought of it horrified them.

Privately Mary knew how they felt. She swallowed her nervousness and tied an end of the thinnest, lightest line to one of her arrows, and sent it flying upward from the bow.

She lost the first arrow: it stuck in the bark partway up and wouldn't come out. She lost the second because, although it did clear the branch, it didn't fall far enough to reach the ground on the other side, and pulling it back, she caught it and snapped it. The long line fell back attached to the broken shaft, and she tried again with the third and last, and this time it worked.

Pulling carefully and steadily so as not to snag the line and break it, she hauled the prepared rope up and over until both ends were on the ground. Then she tied them both securely to a massive buttress of one of the roots, as thick around as her own hips. So it should be fairly solid, she thought. It had better be. What she couldn't tell from the ground, of course, was what kind of branch the whole thing, including her, would be depending on. Unlike climbing on rock, where you could fasten the rope to pitons on the cliff face every few yards so you never had far to fall, this business involved one very long free length of rope, and one very long fall if anything went wrong. To make herself a little more secure, she braided together three small ropes into a harness, and passed it around both hanging ends of the main rope with a loose knot that she could tighten the moment she began to slip.

Mary put her foot in the first sling and began to climb.

She reached the canopy in less time than she'd anticipated. The climbing was straightforward, the rope was kindly on her hands, and although she hadn't wanted to think about the problem of getting on top of the first branch, she found that the deep fissures in the bark helped her to get a solid purchase and feel secure. In fact, only fifteen minutes after she'd left the ground, she was standing on the first branch and planning her route to the next.

She had brought two more coils of rope with her, intending to make a web of fixed lines to serve in place of the pitons and anchors and "friends" and other hardware she relied on when climbing a rock face. Tying them in place took her some minutes more, and once she'd secured herself, she chose what looked like the most promising branch, coiled her spare rope again, and set off.

After ten minutes' careful climbing she found herself right in the thickest part of the canopy. She could reach the long leaves and run them through her hands; she found flower after flower, off-white and absurdly small, each growing the little coin-sized thing that would later become one of those great iron-hard seedpods.

She reached a comfortable spot where three branches forked, tied the rope securely, adjusted her harness, and rested.

Through the gaps in the leaves, she could see the blue sea, clear and sparkling as far as the horizon; and in the other direction over her right shoulder, she could see the succession of low rises in the gold-brown prairie, laced across by the black highways.

There was a light breeze, which lifted a faint scent out of the flowers and rustled the stiff leaves, and Mary imagined a huge, dim benevolence holding her up, like a pair of giant hands. As she lay in the fork of the great branches, she felt a kind of bliss she had only felt once before; and that was not when she made her vows as a nun.

Eventually she was brought back to her normal state of mind by a cramp in her right ankle, which was resting awkwardly in the crook of the fork. She eased it away and turned her attention to the task, still dizzy from the sense of oceanic gladness that surrounded her.

She'd explained to the mulefa how she had to hold the sap-lacquer plates a hand span apart in order to see the sraf and at once they'd seen the problem and made a short tube of bamboo, fixing the amber-colored plates at each end like a telescope. This spyglass was tucked in her breast pocket, and she took it out now. When she looked through it, she saw those drifting golden sparkles, the sraf, the Shadows, Lyra's Dust, like a vast cloud of tiny beings floating through the wind. For the most part they drifted randomly like dust motes in a shaft of sunlight, or molecules in a glass of water.

For the most part.

But the longer she looked, the more she began to see another kind of motion. Underlying the random drifting was a deeper, slower, universal movement, out from the land toward the sea.

Well, that was curious. Securing herself to one of her fixed ropes, she crawled out along a horizontal branch, looking closely at all the flower heads she could find. And presently she began to see what was happening. She watched and waited till she was perfectly sure, and then began the careful, lengthy, strenuous process of climbing down.

Mary found the mulefa in a fearful state, having suffered a thousand anxieties for their friend so far off the ground.

Atal was especially relieved, and touched her nervously all over with her trunk, uttering gentle whinnies of pleasure to find her safe, and carrying her swiftly down to the settlement along with a dozen or so others.

As soon as they came over the brow of the hill, the call went out among those in the village, and by the time they reached the speaking ground, the throng was so thick that Mary guessed there were many visitors from elsewhere, come to hear what she said. She wished she had better news for them.

The old zalif Sattamax mounted the platform and welcomed her warmly, and she responded with all the mulefa courtesy she could remember. As soon as the greetings were over, she began to speak.

Haltingly and with many roundabout phrasings, she said:

My good friends, I have been into the high canopy of your trees and looked closely at the growing leaves and the young flowers and the seedpods.

I could see that there is a current of sraf high in the treetops, she went on, and it moves against the wind. The air is moving inland off the sea, but the sraf is moving slowly against it. Can you see that from the ground? Because I could not.

No, said Sattamax. That is the first we ever heard about that.

Well, she continued, the trees are filtering the sraf as it moves through them, and some of it is attracted to the flowers. I could see it happening: the flowers are turned upward, and if the sraf were failing straight down, it would enter their petals and fertilize them like pollen from the stars.

But the sraf isn't falling down, it's moving out toward the sea. When a flower happens to be facing the land, the sraf can enter it. That's why there are still some seedpods growing. But most of them face upward, and the sraf just drifts past without entering. The flowers must have evolved like that because in the past all the sraf fell straight down. Something has happened to the sraf, not to the trees. And you can only see that current from high up, which is why you never knew about it.

So if you want to save the trees, and mulefa life, we must find out why the sraf is doing that. I can't think of away yet, but I will try.

She saw many of them craning to look upward at this drift of Dust. But from the ground you couldn't see it: she looked through the spyglass herself, but the dense blue of the sky was all she could see.

They spoke for a long time, trying to recall any mention of the sraf wind among their legends and histories, but there was none. All they had ever known was that sraf came from the stars, as it had always done.

Finally they asked if she had any more ideas, and she said:

I need to make more observations. I need to find out whether the wind goes always in that direction or whether it alters like the air currents during the day and the night. So I need to spend more time in the treetops, and sleep up there and observe at night. I will need your help to build a platform of some kind so I can sleep safely. But we do need more observations.

The mulefa, practical and anxious to find out, offered at once to build her whatever she needed. They knew the techniques of using pulleys and tackle, and presently one suggested a way of lifting Mary easily into the canopy so as to save her the dangerous labor of climbing.

Glad to have something to do, they set about gathering materials at once, braiding and tying and lashing spars and ropes and lines under her guidance, and assembling everything she needed for a treetop observation platform.

After speaking to the old couple by the olive grove, Father Gomez lost the track. He spent several days searching and inquiring in every direction, but the woman seemed to have vanished completely.

He would never have given up, although it was discouraging; the crucifix around his neck and the rifle at his back were twin tokens of his absolute determination to complete the task.

But it would have taken him much longer if it hadn't been for a difference in the weather. In the world he was in, it was hot and dry, and he was increasingly thirsty; and seeing a wet patch of rock at the top of a scree, he climbed up to see if there was a spring there. There wasn't, but in the world of the wheel-pod trees, there had just been a shower of rain; and so it was that he discovered the window and found where Mary had gone.