'He speaks truth, my Lord,' said Vennel in Quya. 'His office is guaranteed inviolable by the Wise.'

Ignoring Vennel, Aurum said to the courier, 'You will give me what you carry or else I will have it taken from your corpse.' He made a circling motion with his hands and Marula lance heads appeared at the man's throat. The man licked his lips as he looked into their pitiless yellow eyes. Trembling, he fumbled off one of his gloves and reached behind him to unfasten a packet. He looked at it, hesitated, then handed it to Aurum.

The Master took the packet and turned away. 'Destroy him,' he said.

'But, my Lord…' cried Vennel.

Carnelian watched the stabbing, blinking at every thrust.

'I will take all the responsibility,' he heard Aurum say. The Master flicked his hand and the courier's gory body was hurled over the parapet, then he mounted and began to accelerate off down the road.

At the next tower they were met by consternation. As the changeover was made, Aurum secluded himself in the tower with its keeper. Carnelian looked in both directions for signals from the neighbouring towers. Aurum returned and, saving nothing, led them off down the road. As he rode, Carnelian looked for and found the usual signal sent ahead to announce their coming to the watch-towers further down the leftway. But that was not all. A long and complex communication followed, flashed from the tower they had just left. He wondered what message was being sent soundlessly through the air to the Wise in Osrakum.

Thrice more they stopped and thrice more set off again, coursing down the white road that split the world in half. On and on they flew until the sky darkened to night and they slowed, almost blind, lured by a star that seemed to have fallen to the ground.

The star was a beacon that a watch-tower held aloft. A belt of flames round its waist exaggerated its black mass and cast a lurid glow up into the undersides of its arms. Figures huddled across the bridge, dwarfed by the torso of the tower.

The Masters slowed and clattered over the bridge. Carnelian gazed out over the light-apron of an encampment that spread round the tower. Beyond its glittering edge there was only night.

As they dismounted the keeper came towards them.

'Masters, we are unworthy,' he said, as he and the auxiliaries behind him knelt.

Aurum swelled vast before him. 'Everything is ready?'

'All your instructions have been precisely obeyed, my Master. I oversaw the cleansing myself.'

Aurum swept past him with the others. Carnelian took one look up at the three huge ribs above him, then followed the others behind the monolith into the tower.

As Carnelian let the quartz beads slide along the abacus strings they made an annoying clink. He angled the frame the other way and grimaced at the sound. He was thinking about his father. His feelings were in turmoil. Clink. Clink. He put the abacus down with a crack on the table and lifted the lamp to look round the cell. It reminded him of the cabin in the baran though it was not so small. He stretched himself out on the sleeping platform. It ran out at his knees. The ceiling was formed by a long barrel of wood that ran diagonally across the cell. He guessed that it was the root of one of the tower's wooden arms. He kept on seeing his bloodied father. Then he had felt such loss and had been unable to show it. Now the love he bore his father had cooled again and Crail's blood still trickled between them.

A knock on the door made him sit up and reach for his mask. He held it before his face. 'Come.'

The door opened and something like the ghost of his brother Tain slipped in. Carnelian dropped the mask and they looked at each other. Carnelian forced a smile. He could not bear to see him look so limp. He reached out and pulled him into a hug. He winced when he found Tain was like something made of wood.

He let him go and blustered, 'I should've expected it. Now that I'm free of the other Master, I can have you back.' The reek of incense coming off Tain was stronger than that which still clung to the cell from its fumigation. They cleaned you?'

'I had to be purified before approaching a Master,' said Tain with no change of expression.

Carnelian nodded, searching for words.

'Is the Master OK?' Tain said at last.

'He says so.'

More silence.

'He has no-one to tend to him,' said Tain. Carnelian remembered the boy that Aurum had handed over to be killed. 'Would you mind… ?' 'No,' said Tain, and began to open the door. 'Please come back… after you've seen him…' Tain nodded without turning, then left.

While he waited, Carnelian busied himself by rummaging through the cell. He found a small cupboard recessed into the wall that gave off a waft of ink as he opened it. The shelves inside were neatly stacked. Some folding parchments in a rack were crammed with geometrical figures, calculations, tables solid with symbols. A tube holding writing styluses stood beside jars of ink. Most curious of all were strange instruments, organisms of brass and bone, with hinged arms and shell edges filigreed with numbers. All these things confirmed his belief that he had been given the cell of one of the watch-tower ammonites.

He knelt on the bed to peer through a slit in the wall. His eyes filled with the glimmers of the encampment. He was in the tower's upper storey. There were two more below him, and then the entrance hall with its cistern. He pushed his face into the slit to breathe in the cooking smells, the warm stink of beasts that overlaid the cloying odour of the land.

The door opened behind him and he turned to see Tain looking ashen.

'Father?' Carnelian gasped.

'He's fine, the wound's not too deep, but the bandages that have soaked up the blood are rotting.' Tain scrunched up his nose.

'I'll go to him,' said Carnelian, crossing the cell.

Tain took his arm. 'You'd better let him sleep, Carnie.'

Carnelian reached up to trap his brother's hand against his arm so that he could not pull it away. He examined the narrow face. His little brother had the look of an old man. Their eyes meshed. Carnelian searched Tain's, thinking about Jaspar's price. He wanted to say something but could not find a single word.

Tain gently pulled his hand away and walked over to the bed and started stroking out the creases. His hands looked painfully thin. Carnelian had to have some air and so he put on his mask and left the cell.

Three sides of the hall had wooden walls into which were set the doors that led into the other cells. The fourth side was formed by the tower's outer wall. Against its stone was the ladder they had pulled up after them when they had left the Marula in the dormitory storey below. On either side dangled the counterweights that kept it in place. Perhaps as an attempt at humour, these had been shaped like men around whose necks the cables were attached. Beside the ladder were the cables that went down to a longer ladder they had climbed from the entrance hall, past the grooms' dormitory and into that of the auxiliaries below. Its counterweights were strung up with their heads touching the ceiling. The keel-beam ran over his head and buried itself in the opposite wall. The six ribs coming through the plaster embedded themselves three to each side, in the beam. The whole construction looked like the underside of a grasshopper.

The floor boxed in by the wooden walls was formed into a cross by the four hatches cut into its corners. Carnelian went to the centre of this cross and peered at the doors that lay at the ends of the arms. Each had an eye daubed on it but only one door, apart from his, had the chameleon. He crept to that, listened but could hear nothing. The desire to see his father was tempered by a fear of disturbing his rest. Their meeting would be painful for both of them. An angry voice rang out. Though muffled, it was still clearly Jaspar's. Carnelian heard a slap and flinched. Maybe it was the attack that had made Jaspar lose so much composure as to actually strike a slave with his own hand.