‘Yes,’ she said softly. ‘But …’

The Aachim will know what to do.

Tiaan explained to Haani what they were looking for. Minis’s directions proved beautifully clear, though the distances were shorter than he’d estimated. They found the fault, and the opening beyond it, after the middle of the day. Tiaan had to take off her pack to get in, the entrance being nearly blocked with ice. At the other end the wall was also crusted with ice and a thin layer of white, crystallised from seepage through the rocks. She slapped the face in the rhythm Minis had taught her. Nothing happened. She did it again. Still nothing. Frowning, Tiaan sat back.

‘Maybe the door is stuck,’ said Haani.

‘Of course! The edges are cemented up. Give me a hand, Haani.’

They tapped all around with pieces of rock, cracking the coating of ice and crystals off. The door still did not move and Tiaan had to clean out the gaps with a chisel from her toolkit. As soon as the last fragment fell, the door scraped up. Tiaan and Haani hurried through, in case it snapped down again. Light flared above them, coming from a glossy globe on the wall. Tiaan had not seen anything like it before, and it bothered her, though she had read about the clever Aachim in the Histories and knew their craft was greater than humankind’s.

As they were donning their packs, Haani said, ‘What’s that?’

It was a dull clanging, far away. ‘I don’t know,’ said Tiaan. ‘Perhaps an alarm. Well, they’ll certainly know we’re coming.’

They were in a large tunnel with smooth walls of tormented schist. Mica sparkled here and there. They kept going, following Minis’s instructions, and emerged through the final door into a cavern. Ahead, a stone stair wound up. Tiaan led the way. After the equivalent of five long flights, they came out in a stone-lined room.

‘I don’t see any glass gong,’ said Haani. Tiaan had told her about that.

‘We have to keep going up, I suppose.’

Outside, they trudged down a long corridor before emerging in a shell-shaped chamber, at least a hundred spans long, cut out of the twisted and knotted rock of Tirthrax. Tiaan just wanted the journey to end. Haani, though exhausted, plodded on without complaint.

To their left was another stair, a tight spiral of crystal treads held in place by wires. It looked too delicate to take their weight. ‘This must be it,’ Tiaan said doubtfully.

She put one foot on the lowest tread. It did not move; the stair was more solid than it looked. Lights came on above. Another alarm pealed, a higher note than the first, but there was no sign of life. No doubt they lived further up, since Minis had told her to go all that way.

The stairs kept going, floor after floor. There seemed no end to them and Tiaan was staggering long before the top. They rested on the wires, then continued, following the lights which went on above and off below. Other alarms sounded, pitched high and low, until the whole place echoed with them. The first stopped after an hour, so Tiaan supposed the others would, too.

It must have been three hours’ climb before they found themselves at the low end of another enormous chamber. This one was egg-shaped, decorated with strange arts and furnished here and there, equally strangely. Before them stood the glass gong, twice Tiaan’s height. A leather-coated wooden mallet sat beside it. Taking up the mallet, she struck the gong fair in the middle. It issued forth a low, trembly sound that she could feel vibrating in her bones.

A hundred alarms went off at once. Tiaan laid down the mallet and waited. And waited.

No one came. She struck the gong over and over. The result was the same. No one answered the call, not after an hour, or two hours, or four, or eight, or sixteen. Eventually the alarms stopped.

In the morning Tiaan struck the gong again and again. Haani did too. There was no response. Finally, in the middle of the night, after they had been in Tirthrax for a good thirty hours, Tiaan was forced to conclude that the Aachim, who had lived here for thousands of years, dwelt here no longer. The whole vast edifice of Tirthrax, the greatest city they had ever made, had been abandoned.

FIFTY-FIVE

The morning after his idea about the balloon, Nish was hauled into a meeting room to find every artificer and artisan in the manufactory there, as well as a short, plump woman Nish had never seen before. She had stringy hair, thinning on top; her clothes were distinctly shabby and not very clean. Nish wondered what a scrubwoman was doing at the meeting, for so he judged her to be. He prided himself on his own appearance.

‘This is Mechanician M’lainte,’ said the scrutator. ‘I sent a skeet for her and she came in the night.’

Nish gaped, and immediately wished he hadn’t, for Xervish Flydd was staring right at him. That this shabby creature could be the great mechanician was remarkable enough. That the scrutator had got her here so quickly was astounding. Even if a message had been sent to Tiksi by skeet straight away, it could hardly have found M’lainte before three in the morning. It was only eight now, so she must have travelled the road in the winter dark. That made her a lot braver than he was.

‘M’lainte,’ said the scrutator, ‘please speak.’

‘We are assembled to discuss an urgent new project,’ said the mechanician. She held up a large drawing, clearly based on the sketches Nish had done last night. ‘That is, to build an air floater, like an enormous child’s balloon. One large enough to carry people through the air for …’ She looked to Xervish.

‘A hundred leagues, if necessary.’

‘Just so! The balloon would be lifted by hot air from a stove.’ M’lainte indicated a box hanging just below the inverted teardrop of the balloon. Below that was suspended a wickerwork basket.

After a long silence, everyone spoke at once.

‘It can’t be done!’ A loud voice from the back overrode the others.

‘Oh?’ said the mechanician coolly. ‘Says who?’

‘I am Porthis, senior artificer.’

‘And noted jeremiah,’ Nish muttered to Irisis. Porthis had made his life miserable since Nish had arrived here.

‘What is your objection, Porthis?’ asked the mechanician.

‘The balloon would have to be enormous to lift such a weight. Maybe the height of the manufactory walls.’

‘That’s correct,’ said M’lainte.

‘The wind would tear it apart.’

‘It’s not fixed! The wind carries it. Besides, it would be built strongly.’ She showed a drawing of the reinforcing – fine cables and strategically placed braces. ‘If you judge this to be deficient, I challenge you to produce a better design.’

Porthis was not deflated. ‘The hot air will go cold and the balloon will fall, killing everyone in it.’

‘Thus the stove, which displaces the cooling air with more heat.’

‘Will set fire to the balloon.’

‘See here – I have marked in a protective flue.’

‘In that case it will be too heavy.’

‘Then, Senior Artificer Porthis, you will be in charge of making it lighter! And you will go on the first test flight, so make it strong and safe as well. Artificers all, I want to see a finished drawing for a trial balloon, tonight after dinner. I’ve already sent to Tiksi for materials. We’ll begin making it in the morning.’

Three days after Ullii had first seen Tiaan, she lost her.

‘I sensed her,’ she said to the scrutator and Nish in the afternoon. They were in a dim room and Ullii was not wearing mask or goggles. The scrutator liked to see her eyes when he spoke to her. ‘I saw her crystal more clearly than ever before. I could almost see her, and clawers, lots of them. They were flesh-forming. It was horrible! I saw a creature they made. It wanted to eat her.’ Ullii sprang up and paced across the room.