Mary couldn't sleep. Every time she closed her eyes, something made her sway and lurch as if she were at the brink of a precipice, and she snapped awake, tense with fear.

This happened three, four, five times, until she realized that sleep was not going to come; so she got up and dressed quietly, and stepped out of the house and away from the tree with its tentlike branches under which Will and Lyra were sleeping.

The moon was bright and high in the sky. There was a lively wind, and the great landscape was mottled with cloud-shadows, moving, Mary thought, like the migration of some herd of unimaginable beasts. But animals migrated for a purpose; when you saw herds of reindeer moving across the tundra, or wildebeest crossing the savanna, you knew they were going where the food was, or to places where it was good to mate and bear offspring. Their movement had a meaning. These clouds were moving as the result of pure chance, the effect of utterly random events at the level of atoms and molecules; their shadows speeding over the grassland had no meaning at all.

Nevertheless, they looked as if they did. They looked tense and driven with purpose. The whole night did. Mary felt it, too, except that she didn't know what that purpose was. But unlike her, the clouds seemed to know what they were doing and why, and the wind knew, and the grass knew. The entire world was alive and conscious.

Mary climbed the slope and looked back across the marshes, where the incoming tide laced a brilliant silver through the glistening dark of the mudflats and the reed beds. The cloud-shadows were very clear down there; they looked as if they were fleeing something frightful behind them, or hastening to embrace something wonderful ahead. But what that was, Mary would never know.

She turned toward the grove where her climbing tree stood. It was twenty minutes' walk away; she could see it clearly, towering high and tossing its great head in a dialogue with the urgent wind. They had things to say, and she couldn't hear them.

She hurried toward it, moved by the excitement of the night, and desperate to join in. This was the very thing she'd told Will about when he asked if she missed God: it was the sense that the whole universe was alive, and that everything was connected to everything else by threads of meaning. When she'd been a Christian, she had felt connected, too; but when she left the Church, she felt loose and free and light, in a universe without purpose.

And then had come the discovery of the Shadows and her journey into another world, and now this vivid night, and it was plain that everything was throbbing with purpose and meaning, but she was cut off from it. And it was impossible to find a connection, because there was no God.

Half in exultation and half in despair, she resolved to climb her tree and try once again to lose herself in the Dust.

But before she'd even gone halfway to the grove she heard a different sound among the lashing of the leaves and the streaming of the wind through the grass. Something was groaning, a deep, somber note like an organ. And above that, the sound of cracking - snapping and breaking - and the squeal and scream of wood on wood.

Surely it couldn't be her tree?

She stopped where she was, in the open grassland, with the wind lashing her face and the cloud-shadows racing past her and the tall grasses whipping her thighs, and watched the canopy of the grove. Boughs groaned, twigs snapped, great balks of green wood snapped off like dry sticks and fell all the long way to the ground, and then the crown itself - the crown of the very tree she knew so well - leaned and leaned and slowly began to topple.

Every fiber in the trunk, the bark, the roots seemed to cry out separately against this murder. But it fell and fell, all the great length of it smashed its way out of the grove and seemed to lean toward Mary before crashing into the ground like a wave against a breakwater; and the colossal trunk rebounded up a little way, and settled down finally, with a groaning of torn wood.

She ran up to touch the tossing leaves. There was her rope; there were the splintered ruins of her platform. Her heart thudding painfully, she climbed in among the fallen branches, hauling herself through the familiar boughs at their unfamiliar angles, and balanced herself as high up as she could get.

She braced herself against a branch and took out the spyglass. Through it she saw two quite different movements in the sky.

One was that of the clouds, driven across the moon in one direction, and the other was that of the stream of Dust, seeming to cross it in quite another.

And of the two, the Dust was flowing more quickly and at much greater volume. In fact, the whole sky seemed to be flowing with it, a great inexorable flood pouring out of the world, out of all the worlds, into some ultimate emptiness.

Slowly, as if they were moving themselves in her mind, things joined up.

Will and Lyra had said that the subtle knife was three hundred years old at least. So the old man in the tower had told them.

The mulefa had told her that the sraf, which had nurtured their lives and their world for thirty-three thousand years, had begun to fail just over three hundred years ago.

According to Will, the Guild of the Torre degli Angeli, the owners of the subtle knife, had been careless; they hadn't always closed the windows they opened. Well, Mary had found one, after all, and there must be many others.

Suppose that all this time, little by little, Dust had been leaking out of the wounds the subtle knife had made in nature...

She felt dizzy, and it wasn't only the swaying and rising and falling of the branches she was wedged among. She put the spyglass carefully in her pocket and hooked her arms over the branch in front, gazing at the sky, the moon, the scudding clouds.

The subtle knife was responsible for the small-scale, low-level leakage. It was damaging, and the universe was suffering because of it, and she must talk to Will and Lyra and find a way to stop it.

But the vast flood in the sky was another matter entirely. That was new, and it was catastrophic. And if it wasn't stopped, all conscious life would come to an end. As the mulefa had shown her, Dust came into being when living things became conscious of themselves; but it needed some feedback system to reinforce it and make it safe, as the mulefa had their wheels and the oil from the trees. Without something like that, it would all vanish. Thought, imagination, feeling, would all wither and blow away, leaving nothing but a brutish automatism; and that brief period when life was conscious of itself would flicker out like a candle in every one of the billions of worlds where it had burned brightly.

Mary felt the burden of it keenly. It felt like age. She felt eighty years old, worn out and weary and longing to die.

She climbed heavily out of the branches of the great fallen tree, and with the wind still wild in the leaves and the grass and her hair, set off back to the village.

At the summit of the slope she looked for the last time at the Dust stream, with the clouds and the wind blowing across it and the moon standing firm in the middle.

And then she saw what they were doing, at last: she saw what that great urgent purpose was.

They were trying to hold back the Dust flood. They were striving to put some barriers up against the terrible stream: wind, moon, clouds, leaves, grass, all those lovely things were crying out and hurling themselves into the struggle to keep the shadow particles in this universe, which they so enriched.

Matter loved Dust. It didn't want to see it go. That was the meaning of this night, and it was Mary's meaning, too.

Had she thought there was no meaning in life, no purpose, when God had gone? Yes, she had thought that.

"Well, there is now," she said aloud, and again, louder: "There is now!"

As she looked again at the clouds and the moon in the Dust flow, they looked as frail and doomed as a dam of little twigs and tiny pebbles trying to hold back the Mississippi. But they were trying, all the same. They'd go on trying till the end of everything.

How long she stayed out, Mary didn't know. When the intensity of her feeling began to subside, and exhaustion took its place, she made her way slowly down the hill toward the village.

And when she was halfway down, near a little grove of knot-wood bushes, she saw something strange out on the mudflats. There was a glow of white, a steady movement: something coming up with the tide.

She stood still, gazing intently. It couldn't be the tualapi, because they always moved in a flock, and this was on its own. But everything about it was the same - the sail-like wings, the long neck - it was one of the birds, no doubt about it. She had never heard of their moving about alone, and she hesitated before running down to warn the villagers, because the thing had stopped, in any case. It was floating on the water close to the path.

And it was coming apart... No, something was getting off its back.

The something was a man.

She could see him quite clearly, even at that distance; the moonlight was brilliant, and her eyes were adjusted to it. She looked through the spyglass, and put the matter beyond doubt: it was a human figure, radiating Dust.

He was carrying something: a long stick of some kind. He came along the path quickly and easily, not running, but moving like an athlete or a hunter. He was dressed in simple dark clothes that would normally conceal him well; but through the spyglass he showed up as if he were under a spotlight.

And as he came closer to the village, she realized what that stick was. He was carrying a rifle.

She felt as if someone had poured icy water over her heart. Every separate hair on her flesh stirred.

She was too far away to do anything: even if she'd shouted, he wouldn't have heard. She had to watch as he stepped into the village, looking to the left and right, stopping every so often to listen, moving from house to house.

Mary's mind felt like the moon and the clouds trying to hold back the Dust as she cried out silently: Don't look under the tree - go away from the tree -

But he moved closer and closer to it, finally stopping outside her own house. She couldn't bear it; she put the spyglass in her pocket and began to run down the slope. She was about to call out, anything, a wild cry, but just in time she realized that it might wake Will or Lyra and make them reveal themselves, and she choked it back.

Then, because she couldn't bear not knowing what the man was doing, she stopped and fumbled for the spyglass again, and had to stand still while she looked through it.

He was opening the door of her house. He was going inside it. He vanished from sight, although there was a stir in the Dust he left behind, like smoke when a hand is passed through it. Mary waited for an endless minute, and then he appeared again.

He stood in her doorway, looking around slowly from left to right, and his gaze swept past the tree.

Then he stepped off the threshold and stood still, almost at a loss. Mary was suddenly conscious of how exposed she was on the bare hillside, an easy rifle shot away, but he was only interested in the village; and when another minute or so had gone by, he turned and walked quietly away.

She watched every step he took down the river path, and saw quite clearly how he stepped onto the bird's back and sat cross-legged as it turned to glide away. Five minutes later they were lost to sight.