As the mag-lev had approached Ash Border, they all roused themselves to see what one of these frontier towns looked like, for none of them had ventured beyond the hives of Mars's more populated regions.

Though Rho-mu 31 claimed not to be expecting any trouble, Dalia read his threat auspex switch to active as they came within range of the settlement's network antenna. She didn't mention that fact to the others.

Ash Border had proved to be both exotic and slightly dull at the same time, with dusty ore silos, rusted salvage barns and tall drilling machinery dominating the skyline. But with the memory of a Mechanicum forge still bright in their minds, the minor industrial complex of Ash Border seemed small and underwhelming.

The inhabitants were sullen-faced men and women with weather-beaten faces and clothes scoured identical by coarse ash. They offered no welcome and disappeared back to their ramshackle dwellings as soon as their cargo was unloaded by a handful of archaic lifter-servitors.

Dune Town lived up to its name and proved to be no less prosaic, with even more outmoded servitors unloading the allocated inventory before the mag-lev set off towards Crater Edge.

By now they had been travelling for a day and a half. Tiredness was beginning to tell and sleep was hard to come by. Though the ride was smooth, the compartment's seats had been designed with functional practicality in mind rather than comfort.

None of them had been able to muster much enthusiasm to watch Zouche's projection of the view from the driver's compartment as they approached Crater Edge, but when the mag-lev halted at the raised dock, it was quickly evident that something was different.

The place was abandoned. The dwellings were empty and the streets deserted, but it was impossible to tell whether the inhabitants had been driven away or left of their own volition.

The mag-lev was on an automated schedule, so the mystery went unexplained, and the mining supplies allocated for the township remained in the snaking transport's holds as it pulled away.

No sooner had Crater Edge vanished into the dust and haze than Dalia felt a weight she hadn't even been aware of lift from her shoulders, as though some creeping sickness lingered around the township. The place had just felt… wrong.

Not the wrongness of disease or death, but a gurgling hiss of wet code-laughter she caught drifting on the airwaves.

Red Gorge was similarly deserted, the strange whispering code ghosting around it as well. Dalia caught Rho-mu 31 twitching as he heard it too: an insistent scratching that irritated the corners of the mind like an embedded flea.

She caught his eye as the mag-lev pulled away and they saw each other's awareness of the bad code on the air.

Rho-mu 31 shook his head and she took his meaning clearly enough. Say nothing.

At last the mag-lev began the approach to the jagged line of peaks that separated the Tharsis uplands from the magnificent expanse of the Syria Planum. After a long, looping journey southwards, the mag-lev turned north to begin the slow climb over the upthrust spires of rock pushed up and over one another in an ongoing geological collision. The skies beyond the escarpment were dark and shot through with scarlet lightning, as though a great firestorm was brewing.

It had been a long journey and the sight of the two deserted townships had unsettled everyone. They had all heard tales of settlements abandoned when the ore or whatever had originally drawn the settlers there had dried up, but Red Gorge and Crater Edge hadn't felt abandoned, they had felt empty, as though the people there had just vanished. Gone in a heartbeat.

'Perhaps they were pressganged?' suggested Severine. 'I've heard of that. A forge master isn't going to meet his quota and sends his Protectors out into the wastelands to capture more people to work in their forges.'

'Don't be ridiculous,' said Caxton. 'That's just scare stories.'

'Is it?' challenged Severine. 'How do you know?'

'I just do, all right?'

'Oh, well I feel better already.'

'What do you say, Rho-mu 31?' asked Zouche in a tone of doom-laden theatrics. 'Has Adept Zeth ever sent you off to procure slaves to toil in her volcanic forge?'

'From time to time,' admitted the Protector.

That shut them all up.

'You're joking, right?' said Caxton. 'Tell me you're joking.'

'I am Mechanicum,' said Rho-mu 31. 'We never joke.'

Dalia looked into the green orbs of Rho-mu 31's eyes, and though they were devoid of anything resembling humanity, she saw the wry amusement written in his electrical field. She smiled at the horrified expressions on her friends' faces and turned away so as not to spoil Rho-mu 31's fun.

'That's… that's terrible,' said Severine. 'The Mechanicum uses slaves?' was Caxton's disgusted comment.

'I thought more of you, Rho-mu 31,' said Zouche. 'I thought more of Adept Zeth.'

When he judged the silence had gone on long enough, Rho-mu 31 leaned menacingly towards them and said, 'Got you!'

A moment's stunned silence followed Rho-mu 31's words, and then the tension in the compartment was suddenly, explosively, relieved by hysterical laughter.

'That wasn't funny,' said Caxton, between laughing and wiping tears from his eyes.

'No,' agreed Severine. 'You shouldn't say things like that.'

'What? Can't I make a joke?' asked Rho-mu 31.

'I think they're just surprised you made one at all,' put in Dalia, looking back into the compartment. 'I don't think they're used to the Mechanicum trying to be funny.'

Rho-mu 31 nodded and said, 'I may be Mechanicum, but I am still human.'

With that, the strange unease that had settled on them at the sight of the deserted townships was dispelled, and they began chatting as animatedly as when they had built the first version of the Akashic reader.

The excitement of the journey into the unknown was rekindled and as the mag-lev made its way uphill, Zouche extended a discreet dendrite and plugged into the compartment's data port, projecting the view from the hull-mounted picter onto the glass of the window.

They eagerly watched the feed as Zouche panned the image around. They saw the desolate plains stretching away to the south and the black smudge on the horizon above the Magma City nearly two thousand kilometres away. At Caxton's request, Zouche returned the view to front-on and the image shimmered as it displayed the silver mag-line carrying them up into the mountains.

Dalia let out a tiny gasp of fear as she saw the mag-line vanish into a gaping, steel-lined cavern mouth that pierced the flanks of the cliffs and led through the rock towards Mondus Gamma.

She took Caxton's hand and gripped it tightly as the tunnel drew nearer, the yawning blackness of it suddenly terrifying.

'What's the matter?' he asked.

'I didn't realise we'd need to go through the darkness,' she said.

'It's just a tunnel,' said Caxton. 'There's nothing to worry about.'

The forces of the Fabricator General came for Adept Zeth several hours before Dalia's mag-lev approached the tunnel connecting the Tharsis uplands with the Syria Planum. A Mechanicum heavy flyer cruised in from the north-west and set down on the statue-lined Typhon Causeway before the Magma City, scorching a score of the marble worthies black with the heat of its enormous jets. The underside of the craft shone with golden light from the bubbling, steaming lava to either side of the wide causeway.

The ungainly aircraft was unarmed, but as it settled on its landing skids, a continuous loop of code streamed from its augmitters on a repeating cycle, demanding that Adept Koriel Zeth present herself by the order of the Fabricator General.

The summons was broadcast in the highest and most authoritative code tense, and as such could not be ignored. The flanks of the flyer gusted steam and folded outwards, providing debarkation ramps for the warriors carried within.