Realising that she was shaking with hunger, Tiaan felt a copper coin out of her purse and trudged down to a barrow boy. There she bought a long spicy sausage baked in pastry and set off for home, nibbling as she walked. The sausage was delicious, hot and with a strong peppery flavour. Just half of it filled her stomach and made her feel better.

It was a slow, slippery climb back up the mountain in the rain. Darkness, which at this time of the year came before five o’clock, was already falling before she saw the lights of the manufactory high above. Tiaan toiled up the last distance, went inside and sat down in her cubicle. The hedron lay there accusingly on the bench. Since she was no closer to a solution than before, Tiaan went looking for Overseer Gi-Had.

‘He’s gone up the mountain,’ said Nod the gateman. ‘Trouble in the tar mine. Poisoned air, I think.’

‘Then he won’t be back today,’ said Tiaan. It was four hours’ walk to the tar mine, each way. ‘Have you seen Gryste?’

‘He’s unblocking the waste drains.’

Going left out the gate, Tiaan followed the earth track around the outside of the manufactory wall. She turned the corner, taking a shortcut between huge stone cisterns excavated into the rock to prevent them freezing solid in the four-month winter. In the space between them she glimpsed a couple locked in passionate embrace. There were so many people in the manufactory, and so little privacy, that even the most inhospitable places were in demand.

The discharge flume from the aqueduct had a curtain of icicles hanging from the lip. In the distance a creche-mother was instructing twenty or thirty of her young charges in the use of a sling. They were firing pebbles at the outline of a winged lyrinx, painted on one of the pillars of the aqueduct.

The path wound past stockyards, barns, slaughterhouses and a butchery. The smell was frightful. Tiaan hurried by a cluster of outbuildings where the weavers and other non-essential tradespeople worked. Around the back, piles of furnace ash were eroding into a gully. A series of stonework pipes dripped noxious fluid over the edge.

She found the foreman by a stand of blazing torches, shouting at a group of blackened navvies hacking tar from one of the pipes. They could only work for a few minutes before the fumes drove them out. Their hands and arms were blistered, their red noses dripping.

‘Excuse me?’ she said hesitantly.

‘Yes?’ snapped Gryste, smacking his sword on his thigh.

‘I need to talk to you. About the cont –’

‘Not here!’ He hauled Tiaan away.

Pulling free, she rubbed her throbbing wrist.

‘You can’t talk in front of the navvies, artisan!’

‘Why not?’

‘Morale is bad enough as it is. They’ll get it wrong, and gossip. Where were you this morning?’

‘I had to go to Tiksi to see my mother.’

‘You did not seek my permission.’

‘I – I’m sorry.’ He would not have given it so Tiaan had not asked, though she was due the time off.

‘I’ve had it with your slacking and your refusal to obey the rules. I’m adding a month to your indenture. If it happens again, six months,’ he growled. ‘What do you want?’

Tiaan could not speak. The punishment was all out of proportion to the crime. It did not occur to her to challenge him; to ask if he had that power.

‘Well, artisan? Don’t waste my time.’

‘I need to know how the controllers failed,’ she said in a rush. ‘Did they go suddenly? What other signs were there? Did anything unusual happen at the same time?’

‘I’ve had a report from the battlefield but it doesn’t say much. The controllers started acting erratically. The field came and went. Some of the clankers’ legs had power, the others not. Then the field failed completely.’

‘Has it happened with clankers built by other manufactories?’

‘No idea. They’re scattered across half a thousand leagues and we don’t have enough skeets to send messages back and forth. The armies have priority.’ With a curt nod, he went back to the drains.

Feeling obstructed at every turn, Tiaan went inside and unlocked the old crafter’s rooms. Everything was exactly as it had been the day Barkus died. The new crafter, when appointed, would take over his offices, but though Tiaan was the senior artisan she had no right to use these rooms. The hierarchy must be maintained. She still laboured in the cubicle she’d had as a prentice.

Tiaan spent hours going through the crafter’s journals, trying to find out if controllers had ever failed this way. Barkus turned out to be the least methodical of men, which was surprising since he’d checked her workbooks and journals every day of her eight-year prenticeship. Nothing was organised, much less indexed or catalogued. The only way to find out if he’d worked on a particular problem was to read everything he’d ever written. That was frustrating too, for he often broke off in the middle of an investigation and never resumed it, or continued in the blank spaces of whatever journal he’d happened to lay his hands on at the time.

She went through the bookshelves, cupboards and pigeonholes crammed with scrolls, but found not a mention of her problem. The desk contained nothing of interest – everything secret had been locked away after Barkus’s death. However, as she pulled out the lowest drawer, it stuck.

It took some time to free it, after which Tiaan removed the drawer to see what was the matter. She was used to fixing things. Probably the runners needed waxing. As she was rubbing them with the stub of a candle, she noticed that the drawer was shallower than its external dimensions indicated. That could only mean one thing.

It did not take her long to find the secret compartment. Inside lay a slim book made of rice paper, with soft leather covers. She picked it up. The title page simply said: Runcible Nunar – The Mancer’s Art.

No wonder Barkus had hidden it. The penalty for having an illegal copy of any book on mancing would be horrific. Nunar’s treatise was justly famous and many copies had been made, though such books were guarded jealously. Why had Barkus, a humble crafter in an obscure manufactory, obtained an illegal copy?

At a footfall outside the door, Tiaan thrust the book into her coat and pushed the drawer in. A cold voice broke into her thoughts.

‘Just what do you think you’re doing?’

‘I beg your pardon?’ Tiaan said. The intruder was Irisis Stirm, a fellow artisan slightly Tiaan’s junior, although Irisis did not think so.

She stood in the doorway, tapping an elegant foot. Irisis knew her worth. Tall and lavishly endowed, with corn-yellow hair and brilliant blue eyes, she stood out in the manufactory like a beacon. Tiaan had never met anyone with hair that colour, and no one around here had blue eyes, though the old crafter’s may have been when he was young.

‘You have no right to come in here. These are the crafter’s rooms. He was my uncle!’ Irisis pointed that out at every opportunity.

‘I answer to Gi-Had, not you! Look to the quality of your own work!’

That was a mistake. Irisis was much better at managing the other artisans than Tiaan was. Moreover, she made controllers of rare perfection and extraordinary beauty – works of art. Her use of crystals, though, was timid, and she was peculiarly sensitive to criticism about it.

‘At least my controllers work!’ Irisis sneered.

‘Only because we all help you tune them.’

‘How dare you!’ Irisis cried. ‘If Uncle Barkus was still alive he’d put you in your place.’

‘He did! He put me above you. Now he’s dead and I am responsible for your work.’

‘Unless,’ Irisis said reflectingly, ‘you’re sent to the breeding factory to do your duty.’

Tiaan had no comeback. Irisis did her duty enthusiastically and often, though so far with no sign of success. Perhaps she used a preventative. That was a serious crime, though not an uncommon one. Heading for the door, Tiaan laughed nervously. ‘I think I’m more valuable here than there!’