Through the floor, Carnelian could feel the quake as Osidian moved further along the bench.

'Hooking out the Cranial Organs.'

'What?' said Carnelian.

'Peh!' said Osidian. These are nothing but manuals of embalming.'

'Is it a secret art?' asked Carnelian, with a sour taste in his mouth.

'One of the most secret.'

'Not something I desire to learn,' said Carnelian, not bothering to hide his disappointment. 'Nor I.'

Carnelian felt suddenly very angry. 'Is that it then?' he asked loudly. A fleshy door closed over his mouth.

'Hush!' whispered Osidian and took his hand away.

'If these are the most secret books in the Library of the Wise,' whispered Carnelian, 'then, my Lord, I am grown weary of their tame marvels.'

A heavy silence fell. He listened for and found the breeze of Osidian's breathing. 'Does my Lord challenge me to find for him a diversion that is less tame?' the darkness said through a smile.

'Well, if-'

Tomorrow, come to the usual place but wear warm clothes and heavy outdoor paint. Tell your people not to expect your return for three days.'

Carnelian looked through the robes Fey had sent him. They were all flimsy, delicate silks, clothing suitable for wearing in his chambers, not for whatever expedition Osidian had in mind. And what was that? He was plagued with speculations. Outdoor paint? Where could Osidian be planning to go that required outdoor paint? For three days? It had to be some region of the Halls of Thunder exposed to the sun. That must be it. No need to worry that he was going against his father's wishes. Still, he was nagged by the thought that it was wrong to go.

'I must,' he said. He knew no way to get a message to Osidian to tell him that he was not coming. How could he just not turn up? He smiled thinking about him. There was still the problem of the robe. He knuckled his forehead. At last, with a sigh, he went to pick up the only outdoor robe he had. He shook out its scarlet mourning brocade, laid it out, then went to the door to call a servant. When the man came he sent him off to fetch body paint.

'Body paint, Master?'

'Body paint.'

The man was soon back with a jar and pads. Carnelian put up with the timorous painting. Once the paint had dried, he put on the mourning robe and finally, his mask.

Outside his chamber, he told his guardsmen that he would be spending three days away from them. When they sneaked glances at each other, he gave them assurances that he would be all right. He had to ignore the pleas in their eyes. After all, he himself did not know where he was going. Their looks of fear made him swear a silent promise that, should it become necessary, he would put himself between them and the Master's wrath. This did not stop him, as he walked away, feeling selfish and hazardous of their care.

Osidian was waiting for him. His eyes widened as Carnelian came closer. 'Is that a mourning robe?'

'It was the only one I had.'

'It is hardly the best omen for our expedition.'

Carnelian did not like Osidian's unfocused stare. 'Where are we going, then?'

Osidian seemed to come awake. 'Down to the Yden.'

Carnelian stared at him in disbelief. The Yden? Down the Rainbow Stair?'

Osidian shook his head. There is another, more ancient way.'

'Another stair?'

Osidian's lips formed an enigmatic smile. 'More a ladder than a stair. The descent is harrowing. Do you feel you have the strength?'

The challenge fired Carnelian up. 'If I do not, then at least I shall have the long pleasure of falling into the Yden like a star.'

Osidian's brow darkened. This is not a children's game, Carnelian. You speak lightly of what you do not know.'

Carnelian was stung to anger but before he could say anything Osidian threw his hands up in appeasement. 'Forgive my tone.' He grinned. Carnelian could not help grinning back. Osidian lowered his head and looked enquiringly at Carnelian.

Carnelian forced solemnity into his face. 'I am certain I have the strength.'

'Well then, let us make haste. When night falls it will not bode well for us should it find us on the Ladder. First we must put on our disguises.'

'Disguises?'

'It would be unwise' – he smirked – 'to go deep into the chambers of the Wise as ourselves.'

Osidian slipped out of the lantern light and returned carrying two packs. As he offered one, Carnelian remembered the Tower in the Sea and his father's anger at him carrying burdens. He realized that Osidian was angry too.

'Does my Lord consider it shameful to bear a pack when I did not consider it so to bring them both here?'

'No, not at all.' Carnelian grabbed one and swung it round onto his shoulder. He was adjusting its straps when Osidian threw him a bundle. Carnelian turned the thick purple silk in his hand. Osidian had already unrolled his and flung it over his back, concealing the pack under it. Carnelian followed his lead, but worried about the hump the pack made. He shrugged when he saw Osidian was unconcerned and pulled the cloak round him, securing its bony hooks. Smoothing it, he touched beadcord. He looked down and saw the panels. He closed his eyes and began to read with his fingers, out loud. The Heart of Thunder is the locus of the rain-heavy sky. It translates along the ritual axis, from the sea. It can be-'

These cloaks are reserved for near-Sapient acolytes. They are a study aid,' said Osidian. 'Come.'

'Our masks?'

Osidian shook his head. 'We must be free of their encumbrance.'

He led them through the moon-eyed door into the library. He opened the lantern, blew it out then put it on the ground, out of the way against a wall.

'Will we not need it further on?' asked Carnelian.

'No,' replied Osidian. Carnelian reached out to take a grip of Osidiah's cloak. He felt his hand being disengaged.

'It will be faster for you to follow your feet,' said the darkness.

Carnelian felt Osidian's cold foot nudging his across the floor to where it was embossed. 'Read it,' said Osidian.

Carnelian used his toe to feel around the shape. 'A face… a horned-ring above… a circle below… bisected thus a sky glyph, thus Sky God.' He returned to feel the face. Its eyes were closed, its mouth open. 'Blowing,' he said. 'It reads as, wind’

'Indeed,' said Osidian, his voice fading into the blackness.

Carnelian followed the wind glyph trail blindly through the library. For a while he had been hearing a whistling up ahead. He bumped into Osidian who gave a groan.

'Hide your face deep in your cowl.'

Carnelian was doing so when a smudging brightness opened in front of them. As he stumbled after Osidian, a gale took hold of his cloak. Carnelian squinted both ways. They were standing near the edge of a ravine. On its further side a smooth heart-stone wall rose up into blackness. Sky light flowed in from the right, where the ravine turned a corner. Left, it narrowed off to a ragged eye-aching blue hole. Here and there narrow bridges arched the drop.

With his hand, Carnelian clamped his cowl onto his head. 'What is this?'

The Windmoat,' cried Osidian and turned into the blast.

They strode leaning into the wind. On their left the stone was as pierced as a sieve. Light blinked through the holes as they walked past. A murmur came through as if from a crowd at prayer. Carnelian paused to glue an eye to one of the holes and saw a tunnel running off into the distance. All the way down one side it was peopled from floor to ceiling with squatting, tallow-faced ammonites. He found the angle to see the tunnel's other side. Stone sloped up to a ledge on which something was sitting in a chair. He could make out a voice, a homunculus, droning, 'Compare cords twenty-five to thirty, Ba-Ta process result spindle for five computations…' He pushed his cheek into the stone, trying to see more. The mummified face of its Sapient master hung above the homunculus, his fingers operating its throat.