In this way, they covered twenty miles a day.

During the third week, it snowed. Ice crusted the rivers, rock cracked and broke above the thousand-foot line of the flanking hills. Cromis found his traps full of white hares and albino foxes with red, intelligent eyes. Birkin Grif killed a snow-leopard with his crutch: for ferocity, it was an even match until the last blow.

For a week, they lived with a community of herders, small, dark-haired folk with strange soft accents, to whom the war in the north and west was but a rumour. They gave the Queen a sheepskin coat, they were shy and kind. As a measure of gratitude, Tomb the dwarf cut wood from dawn to dusk; while Grif sat with his bad leg stretched in front of him, and split it into enough kindling for a year (they became friends again as a result of this: neither of them loved anything better than cutting and chopping).

Everything began to seem distant: the snow was an insulator: Cromis forced himself to keep in mind the defeat in the North. It was important to his brooding nature that he remember the terrible blades of the geteit chemosit. He imagined them. He saw them lay seige to Duirinish in his head. Would the winter halt them at all?

After seven days of that, and a further fortnight of travel in the grim mountains at the southern end of the Rannoch, he was glad to see the arable lands around Lendalfoot and catch a glimpse at last of the grey sea breaking on the dark volcanic beaches of Girvan Bay.

Lendalfoot was a fishing town built of pale fawn stone, a cluster of one-roomed cottages and long drying-sheds, their edges weathered, blurred by accumulations of moss and lichen. Here and there rose the tall white houses of local dignitaries. In the summer, fine pink sand blown off the shifting dunes of Girvan Bay filled its steep, winding streets; the fishwives argued bare-armed in the sun; and creaking carts carried the catch up the Great South Road into Soubridge.

But now the waves bit spitefully the shingle beach. The sea heaved, the mad black gulls fought over the deserted deep-water jetties, and the moored boats jostled one another uneasily.

Determined that news of the Young Queen should not travel North by way of the fish-route, Cromis sent Tomb into Lendal-foot to pose as a solitary 'traveller and gather certain information (he stumped off sulkily, stripped of his power-armour so as not to alarm the fishermen, but refusing to give up his axe) then retired with Methvet Nian and Birkin Grif to a barren basalt hill behind the town.

The dwarf returned jauntily, throwing up and catching a small, wizened apple, which had been given to him (he said) by an old woman. 'She was as dried up as her fruit,'he laughed. 'She must have thought I was a child.'More likely, he had stolen it.

'It was a good thing I went alone: they are frightened and surly down there. News has come down the road to Soubridge.'He crunched the apple. 'The Moidart has taken Low Leedale, thrown down Duirinish – with great loss of life – and now marches on Viriconium.

'Between the Pastel City and Soubridge, the geteit chemosit are abroad by night, killing with no reason.'

He ate the apple core, spat the pips impudently at Birkin Grif – who was sharpening his sword with a piece of sandstone he kept in his belt for that purpose – and lay down on his exoskeleton. 'They have given me directions, more or less precise.'He strapped himself up, rose to his feet, once more a giant. He pointed out over the basalt cliffs, his motors humming.

'Our goal lies East and a little inland. The fishermen cooled further toward me when they learnt of my destination: they have little like of this Cellur. He is seen rarely, an old man. They regard him superstitiously, and call him “The Lord of the Birds”.'

In each of them had grown a compulsion to avoid roads and centres of population: by this, they were driven to travel the wilderness that stretches from Lendalfoot to the Cladich Marshes; a hinterland ruined and botched when the Afternoon Cultures were nothing but a dream in the germ-plasm of an ape; a stony wreckage of deep ravines and long-dormant volcanic vents.

'It is a poor empire I have,'said Methvet Nian, 'win or lose. Everywhere, the death of the landscape. In miniature, the end of the world.'

No one answered her, and she drew her hood over her face.

It had not snowed in the South, but a continual rain lashed the grey and leafless vegetation, glossed the black basalt and pumice, and made its way in the form of agitated streams through the ravines to the sea. At night, electrical flares danced about the summits of the dead volcanoes, and the columnar basalt formations took on the aspect of a giant architecture.

As they went, they were shadowed and haunted by birds -ominous cruciform silhouettes high against the angry sky.

They reached the tower of Cellur in the evening of the second day. Cresting a ridge of pitted dolerite, they came upon the estuary of one of the unnamed rivers that runs from the mountains behind Cladich. Luminous in the fading light, the water spread itself before them like a sheet of metal. High black escarpments dropped sheer to its dark beaches; the cold wind made ephemeral, meaningless patterns on its surface.

Set in the shallows near the western bank was a small domed island, joined to the mainland by a causeway of crumbling stone blocks. It was barmen but for a stand of white, dead pines.

Out of the pines, like a stone finger diminished by distance, rose the tower. It was five-faced, tapering: black. A tiny light shone near its summit, a glow that flickered, came and went. Birds wheeled about it, wailing mournfully, dipping to skim the water – fish-eagles of a curious colour, with wings like cloaks in a gale.

'There is nothing for us here,'said Birkin Grif abruptly. 'Only a lunatic would choose to live here. Those fishermen had the right of it.'

But Cromis, who understood isolation, and was reminded of his own tower among the rowans, of Balamacara, shook his head. 'It is what we came for, Grif. Those birds: look, they are not made of flesh.'He touched the corpse of the iridium vulture hanging from his belt. 'We will go down.'

The estuary was filled with a brown, indecisive light, the island dark and ill-defined, enigmatic. The creaking of the dead pines came clearly across the intervening water on the wind. From a beach composed of fine basalt grit and littered with skull-sized lumps of volcanic glass, they mounted the causeway. Its stones were soapy and rotten; parts of it were submerged under a few inches of water.

They were forced to go in single file, Cromis bringing up the rear. As they drew nearer the island, Tomb the dwarf un-limmmbered his axe; and Grif, drawing his broadsword a little way out of its scabbard, scowled about him as if he suspected a conspiracy against his person on the part of the landscape.

With damp feet, they stood before the tower.

It had been formed in some unimaginable past from a single obsidian monolith two hundred feet long by seventy or eighty in diameter; raised on its end by some lost, enormous trick of engineering; and fused smoothly at its base into the bedrock of the island. Its five facets were sheer and polished; in each was cut twenty tall, severe windows. No sound came from it; the light at its summit had vanished; a stony path led through the ghostly pines to its door.

Tomb the dwarf chuckled gently to himself. 'They built to last,'he said proudly to Cromis, as if he had personally dug the thing up from a desert: 'You can't deny that.'He strutted between the trees, his armour silver and skeletal in the dusk. He reversed his axe and thundered on the door with its haft.

'Come out!'he shouted: 'Come out!'He kicked it, and his metal leg rang with the blow; but no one came. Up above their heads, the fish-eagles made restless circles. Cromis felt Methvet Nian draw closer to him. 'Come on out, Birdmaker!'called Tomb. 'Or I'll chop your gate to matchwood,'he added. 'Oh, I'll carve it!'