Not so his servants, who began screaming and jumping up and down.

Careful,' he called. 'Most likely it's Aachim in that flier.'

'Do they eat folk?' said the always irascible Tyal.

'Of course not.'

'Then they're a damn sight better than the enemy.'

If the Aachim found Gilhaelith he would certainly be imprisoned for keeping the thapter from them; he might even forfeit his life. Should the thapter be possessed by the scrutators, however, he would be swiftly tried for keeping it and the amplimet from Klarm, and as swiftly executed. That fate might await him from Gyrull, too, but surely not until he'd tested the globe. The decision took little time. Of his three possible fates, only remaining at Alcifer offered the chance to complete his life's work.

'Not for me,' muttered Gilhaelith, moving further into the shadows.

'So that's how it is,' roared lyal. 'Look at him, hiding like the craven cur he is! His promises were lies. He's a traitor, as I've always said, and the scrutators will pay handsomely for him. Take Gilhaelith!'

Two of the male servants threw themselves on him, while the others took up cudgels and attacked the pair of lyrinx guards standing in the shade. The women began capering madly in the clearing, waving items of clothing at the thapter, but as Gilhaelith fell a cloaking spell renewed itself and the machine vanished.

Three of the male servants lay bleeding on the ground before the lyrinx were defeated. One was felled by an expertly thrown rock, the other went down under the weight of four humans. A cudgel blow knocked it unconscious.

Gilhaelith was dragged, struggling furiously, out into the open. Someone bound his wrists behind his back with a length of cord. Gilhaelith prayed that there were more lyrinx nearby, or he was finished.

Fifty-two.

Malien came to Tiaan's room that night, very late, looking rather drawn.

'I'm sorry,' she said on entering. 'I should have anticipated their reaction and kept our business till later.'

'Of course your people wouldn't want an outsider at their council,' said Tiaan, who had been watching the patterns ebb and flow in the translucent walls. 'I should have known better than to interrupt.'

'It's just that it showed up their fatal weakness - an inability to agree on anything.' Malien sat on the bed, a rhomboid frame of metal with a mattress as hard as a plank. The other furnishings were equally minimal and unornamented. In Tirthrax, every surface of every object had been decorated. 'It's worse than it was before the council began.'

'Are they like this in everything they do?'

Malien sighed. 'Unfortunately, when they deal with the outside world, yes. In the past we've allowed ourselves to be led to disaster because we lacked the courage to challenge a powerful, charismatic leader, or because we believed the unbelievable of him. The march of folly, I call it, and Tensor's folly became so seared into our consciousness that no one wishes to be leader any more. Every proposition is torn apart in the meeting room. We're so afraid of hubris that we won't act at all; not even when the outside world burns.'

'And Vithis is like Tensor, you said. Has Vithis been here?'

'His envoys have, though not recently. The country is too steep and rugged for constructs and, even from the lowlands of Kalar, west of these mountains, it takes weeks to walk into Stasor. For the coming winter, which is six months long here, it can't be done at all.'

'Except by thapter. Do you know where Vithis is?' A long way away, Tiaan fervently hoped.

'He's gone north to the Foshorn, seized land there and closed the borders. No one knows what he's up to.'

'I was sure he would come after me,' Tiaan said softly.

'Another of our failings, in times of duress, is to retreat into our fastness and shut the world out.'

Tiaan sagged with relief. 'What are you going to do, Malien?'

'I don't know. I may return to Tirthrax, if Harjax will let me.'

'Why wouldn't he?'

'My people want the thapter. To gain such a prize, they may find the courage to act.'

Are you in danger?'

'I hardly think so, though . . .'

Three nights later, Tiaan was lying awake in the dark when the room was shaken gently by an earth trembler. It wasn't the first she'd felt here, but the amplimet, which had hardly changed since she'd escaped from the Aachim's nets, began to blink rapidly. She sat up. The room shook again, violently enough to slide a metal goblet off the table. It rang on the stone floor like a distant alarm and the patterns in the walls went wild for a few seconds before returning to their previous progression. Tiaan thought about investigating the source of the trembler with geomancy, but that would require her to use the amplimet. She'd not touched it since Tirthrax and was reluctant to now. The feeling that it was waiting for something was stronger than ever.

She got out of bed to pick up the goblet, then reached for her hedron. As she touched it the field flashed into her mind, but it was all eaten away on one side as if something was taking massive amounts of power from it. Was this what the amplimet had been waiting for?

Without dressing, she fleeted down the hall to Malien's room. The stone was frigid underfoot, for the Aachim main-tained their city at a temperature considerably lower than Tiaan found comfortable.

She rapped on the door. 'Enter!' said Malien.

Tiaan went in. Malien was sitting at the table with Bilfis, who had a glassy cube in his hands, like a model of Stassor. Coloured patterns moved within it, and on the outside. He was frowning.

Malien was making marks, in the Aachim script, on a complicated diagram. Bilfis rotated the edge of the cube, twisting it so that smaller cubes were revealed, twenty-five to each side. He moved the smaller cubes into a new pattern.

Malien made another series of marks. 'Worse!'

Bilfis set the divination cube down on the table and ran his hands through his hair.

'What is it, Tiaan?' said Malien.

'Just after the earth trembler, the amplimet began to blink, and now something is taking vast amounts of power from the Stassor node. I'm afraid-'

'It's not the amplimet,' said Bilfis. 'My people are building a great defence against attack by thapters or other kinds of flying machines.'

'That's all right then,' said Tiaan. 'Isn't it?'

'We're afraid they'll overload the node, or worse,' said Malien direly. 'If you recall, Tiaan, I mentioned this worry in Tirthrax. But my people won't listen. They're too afraid.'

'Of what?'

Anyone and everyone. Once the secret of flight gets out, and surely that won't take long, Stassor will be vulnerable to attack by a fleet of thapters. Suddenly its isolation will be a disadvantage rather than a protection.'

'I see. And what could be worse than overloading the node?'

'Overloading all the nodes.'

Tiaan looked from one to the other. 'I don't understand.'

'We're not sure we do either,' said Bilfis, 'but we're beginning to think that the nodes might not be separate, as has always been thought, but linked!

Through strong forces that can't be detected,' said Malien. Humanity has already seen the lyrinx drain nodes dry. They normally recover within days of the node-drainer being removed, though we don't understand how that can happen so quickly. It should take years for a node to regenerate the field by itself.'

'Unless,' said Bilfis, 'it's replenished from outside, from other nodes.'

'But that's good, isn't it?' Tiaan searched their faces.

'We thought so, until we heard about the death of the Snizort node' said Bilfis. 'That's bothered me ever since I heard the news. I'm afraid . . .' He looked to Malien. She nodded.

'Yes?' said Tiaan.

'If the nodes are linked, it could be a problem.'

'What do you mean?'

'Every month humanity adds more clankers to the thousands they're already using, along with a myriad of other devices that draw power from the field. The lyrinx do the same, as does Vithis with his thousands of constructs. Now Stassor has embarked on this city-sized shield and just to build it will take much from the node. Maintaining it day after day, year after year, will require far more. It adds up to too much power, taken too quickly, and there's got to be a consequence. It may drain the node dry and, if the nodes are linked, the ones surrounding it as well. Perhaps even the ones surrounding them. You see the danger?'

'I think so . . .' said Tiaan.

'If many nodes fail at once, the great forces that create them will ultimately have to readjust. What's that going to do to the puny creatures clinging to Santhenar's fragile shell?'

'Are you saying that some of the nodes might explode, as at Snizort?' asked Tiaan.

'That's one possibility, and the explosive force could spread to the nodes surrounding them,' said Malien. 'Or the driving forces themselves could become unbalanced, tearing the crust of the world apart. No one knows enough geomancy to tell.'

'Is there any way to find out.'

'That's what we've been talking about.'

'Bilfis and I have put our concerns to the Aachim Syndic,' said Malien the following morning. 'That last earth trembler alarmed them, so we turned the screws. My people aren't happy, but they've agreed to give us what we want, in return for the secret of flight. They want to build their own thapters.'

'Is that wise?' said Tiaan, but regretted it as soon as she'd spoken. She had no right to question Malien.

'I had nothing else to bargain with.'

'What are they giving in return?'

'Everything they know about nodes.'

'You might have demanded that by right,' said Bilfis.

'And they might have stalled me for months,' said Malien. This way we can begin in a week.'

'To do what?' said Tiaan.

'To map the nodes near Stassor, so we can see how they're being affected.'

'Can I come too?' Tiaan was used to being busy but there would be nothing for her to do here. 'I'll do anything that needs doing.'

'I want you to come,' said Malien. 'Indeed, I can't do it without you.'

By the time the Aachim had released the thapter and made a start on building their own, weeks later, Tiaan, Malien and a mapmaker had gone through the archives and produced a series of charts of the mountains surrounding Stassor. These showed all nodes the Aachim knew about.

There were many kinds: weak nodes and strong, steady ones and those whose fields fluctuated wildly or unpre-dictably, or flared up only to die away to nothing. There were occasional double nodes and one triple - which Malien was too perilous to approach - as well as two anti-nodes which were even more dangerous. The anti-nodes may have grown by cannibalising the fields of others, but no one had ever dared approach close enough to find out.

Only then did Tiaan and Malien sit down, with a small glass of the Aachim liquor called syspial in hand, and consider their work. The nodes were not evenly distributed but fell into patterns, groups and aggregations, which in turn were organised into provinces. These often corresponded to geographic features like mountain chains, volcanoes, cliffs or ridges. Not always, though - some nodes were not related to anything on the surface of the earth.

Tiaan took a sip of her drink, which was the colour and flavour of sweet blackberry liqueur, but stingingly spicy-hot. 'Where do nodes come from, anyway?'

'No one has any idea,' said Malien, 'except, possibly, your friend Gilhaelith. He knows more about the natural philosophy of the world than anyone.'

'It's been his life's work.' She wondered if Gilhaelith was still alive; and if so, what he was up to.

The next step was to go out at night in the thapter, mapping the fields of the nodes while Malien flew a course by the moon or the stars, and Bilfis plotted the fields on the chart. Tiaan was forced to use the amplimet, which was always risky now. Once or twice she flew the thapter, and had to use the crystal for that as well. She did not have the talent to fly the thapter the way Malien did.

They spent a tedious month on this work, by which time they had created a map of the area within forty leagues of Stassor. It was very rough, but to refine it would have taken months more, for they learned something new every day: new fields and new nodes, even new kinds of nodes. Tiaan wished she understood them.

By that time, two teams, each one comprising hundreds of Aachim, working day and night, had built a pair of thapters, though only the second of them remained at Stassor: the other machine had flown west a fortnight ago. Tiaan suspected it had been sent on an embassy to Vithis, and she was not looking forward to its return.

The following morning she was in the front meeting room when there was a screeching whine outside and the missing thapter shot past a transparent section of wall, heading for the compressed-ice platform.

'Who's that?' Malien said sharply.

'Tormil,' said Harjax. 'I sent him to make contact with Vithis, and from his haste I'd say he has.' He bent his head to his papers.

Malien's left hand gripped Tiaan's knee under the table and squeezed hard - a warning. She wrote a note on a scrap of paper and passed it to Tiaan. 'Would you take this to Bilfis, please? He's in his room.'

'Of course,' said Tiaan. She rose, bowing to the Aachim, who ignored her as usual, and hurried out.

The operator was in such haste that he had flown his thapter right up to the cubular doors, which were spreading apart as Tiaan went by. He threw himself over the side, almost falling in his haste.

Tiaan made her way to Bilfis's room, and found him sitting at the table, poring over his field maps.

'Malien asked me to give you this.' She passed him the paper.

He scanned it, thrust it into his pocket, rolled the maps and sprang up. 'Take these to Malien's thapter. Act normally. Have you your amplimet?'

'Always.'

Scooping gear from the table, he thrust it into a small pack. A pile on the bed followed it and he tossed the pack over his shoulder.

'What's the matter?' said Tiaan.

'Don't ask stupid questions, just go!'

That alarmed her, for the Aachim of Stassor might be remote, condescending or aloof, but they were invariably polite.