'Lie flat!' Gren called, drawing his knife.

'Boycott chimp goods!' Beauty cried. 'Don't allow Monkey Labour in your factory. Support Imbroglio's Anti-Tripartite scheme!'

The stalker was trampling through shallow water now.

Black wings flashed low overhead, thundering with a whiff of decay across the stalker. Next moment, Beauty had been snatched from its placid circling and was being carried coastwards in mighty talons. As it was borne off, its cry came back pathetically, 'Fight today to save tomorrow. Make the world safe for democracy!' Then the birds had it down among the branches.

With water draining from its slender shanks, the stalker was now wading ashore. Four or five of its kind could be seen doing or about to do the same thing. Their animation, their human-like appearance of purpose, set them apart from the dreariness of their surroundings. The brooding sense of life that impregnated the world Gren and Yattmur had previously known was lacking entirely in these regions. Of that hothouse world, only a shade remained. With the sun lolling on the horizon like a bloody and raped eye upon a slab, twilight prevailed everywhere. In the sky ahead, darkness gathered.

From the sea, life seemed to have died. No monstrous seaweeds fringed the shore, no fish stirred in the rock pools. This desolation was emphasized by the shuddering calm of the ocean, for the stalkers – prompted by instinct – had chosen for their migration a season without storms.

On the land, a similar quietude reigned. The forest still grew, yet it was a forest stunned by shadow and cold, a forest half alive, smothered in the blues and greys of perpetual evening. As they moved about its stunted trunks, the humans looked down to see mildew speckling its foliage. Only at one point did a touch of yellow show brightly. A voice called to them,' Vote srh today, the democratic way!' The heckler machine lay like a broken toy where the birds had left it, with one wing visible amid the tree tops; it called still as they trudged inland, out of earshot.

'When do we stop?' Yattmur whispered.

Gren did not answer; nor did she expect an answer. His face was cold and fixed; he did not even glance towards her. She dug her nails into her palm to keep her anger back, knowing the fault was not his.

Picking their way with care, the stalkers moved above the forest, leaves brushing against their legs or occasionally sweeping their bodies. Always the stalkers marched with the sun behind them, leaving it half-hidden beneath a wilderness of sour foliage. Always they marched towards the darkness that marked the end of the world of light. Once a flock of black vegbirds rose from the treetops and clattered away towards the sun; but the stalkers never faltered.

Despite their fascination, their growing apprehension, the humans eventually had to resign themselves to eating more of their rations. Eventually, too, they had to settle to sleep, huddling up closely at the centre of their perch. And still Gren would not speak.

They slept, and when they woke, coming reluctantly back to the consciousness that was now associated with cold, the view about them had changed – though hardly for the better.

Their stalker was crossing a shallow valley. Darkness stretched beneath them, though one ray of sun lit the vegetable body on which they rode. Forest still covered the ground, a distorted forest that now resembled the newly blind who stagger forward with arms and fingers extended, fright apparent in every feature. Here and there a leaf hung, otherwise the limbs were naked, contorting themselves into grotesque forms as the great solitary tree that had over the ages turned itself into a whole jungle fought to grow where it had never been intended to grow.

The three tummy-bellies shuddered with alarm. They were looking not down but ahead.

'O tummies and tails! Here comes the swallowing-up place of all night for ever. Why did we not sadly happily die long long ago, when we were all together and sweating together was juicily nice so long ago?'

'Be quiet, the pack of you!' Gren shouted, grasping his stick. His voice rang hollow and confused to his ears as it was thrown back by the valley.

'O big little tailless herder, you should have been kind and killed us with killing cruelly long when we could sweat, in the time when we still grew on happy long tails. Now here comes the black old end of the world to chop its jaws over us without tails. Alas the happy sunshine, O poor us!'

He could not stop their cries. Ahead lay the darkness, piled up like layers of slate.

Emphasizing that mottled blackness stood one small hill. It stuck up uncompromisingly before them, bearing the weight of the night on its shattered shoulders. Where the sun struck its upper levels it had a golden touch, the world's last colour of defiance. Beyond it lay obscurity. Already they were climbing its lower slopes. The stalker toiled upwards into light; stretched out across the valley, five more stalkers could be seen, one near, four more half lost in murk.

The stalker was labouring. Yet it climbed up into the sunshine and continued on without pause.

The forest too had come through the valley of shadow. For this it had fought its way through the gloom: to be able to fling its last wave of greenery up the last strip of lit ground. Here, on slopes looking back towards the ever-setting sun, it threw off its blights to grow in something like its old exuberance.

'Perhaps the stalker will stop here,' Yattmur said. 'Do you think it will, Gren?'

'I don't know. Why should I know?'

'It must stop here. How can it go any farther?'

'I don't know, I tell you. I don't know.'

'And your morel?'

'He does not know either. Leave me alone. Wait to see what happens.'

Even the tummy-bellies fell silent, staring about them at the weird scene in mingled fear and hope.

Without giving any indication that it ever meant to stop, the stalker climbed on, creaking up the hill. Its long legs continued to pick a safe course through the foliage, until it dawned on them that wherever it intended to go, it was not stopping here on this last bastion of light and warmth. Now they were at the brow of the hill, yet still it marched, an automatic vegetable thing they suddenly hated.

'I'm going to jump off!' Gren cried, standing up. Yattmur, catching the wildness in his eyes, wondered whether it was he or the morel that spoke. She wrapped her arms round his thighs, crying that he would kill himself. With his stick half lifted to strike her, he paused – the stalker, unpausing, had commenced to climb down the unlit side of the hill.

Just for a moment the sun still shone on them. They had a last glimpse of a world with gold in the dull air, a floor of black foliage, and another stalker looming up on their left flank. Then the shoulder of the hill shrugged upwards, and down they jolted into the world of night. With one voice they gave forth a cry: a cry that echoed into the unseen wastes about them, dying as it fled.

For Yattmur only one interpretation of events was possible. They had stepped out of the world into death.

Dumbly she buried her face into the soft hairy flank of the nearest tummy-belly, until the steadily continued jolting of the stalker persuaded her that she had not entirely lost company with the things that were.

Gren said, grasping at what the morel told him, 'This world is fixed with one half always turned towards the sun... we are moving into the night side, across the terminator... into perpetual dark... '

His teeth were chattering. She clasped him, opening her eyes for the last time to search for sight of his face.

In the darkness it floated, a ghost of a face from which she nevertheless drew comfort. Gren put his arms round the girl, so that they crouched there together with cheeks touching. The posture gave her warmth and courage enough to peer furtively around.