'You have to!' begged Dalia. 'Please! It's only when they go wrong that machines remind you how powerful they are.'

'Three, two, one…' continued the countdown.

'No… Oh, Throne, no!' cried Dalia, turning back to the domed chamber.

Blinding light, brighter than a million suns, flooded the chamber of the Akashic reader as the full might of the Astronomican poured its energies through the coffers and into the blind psykers.

Shouts of alarm and warning klaxons blared almost immediately.

And over it all, Dalia could hear the agonised screaming of Jonas Milus.

The desolate uplands between the volcanoes of the Tharsis Montes were bare of structures or habitation. Any landscape habitually trodden by the god engines of the Legios was crushed flat by the unimaginable weight of the titanic war machines. The only artificial creations were those placed there by Legio servitors to act as target practice.

The land between Ascraeus Mons and Pavonis Mons was rugged and inhospitable, an area of demarcation between two warrior orders who shared a region of Mars but little else. A few of the nomadic vassal tribes that plied the ashen wastelands between the great forges of the adepts had tried to found settlements there, but even they were forced to concede that living in the shadow of the Titan fortresses was untenable.

The great golden gateway of the Legio Tempestus fortress at the end of the Ascraeus Chasmata stood open, and three titanic engines, resplendent in their cobalt blue armour plates, marched out. Kill totems and trailing honour banners billowed on their weapons and from enormous masts fitted to their carapaces.

Metallus Cebrenia, the engine of Princeps Sharaq, led them out, followed by its smaller siblings, the Warhounds Raptoria and Astrus Lux. All three machines were fully armed and ready to fight, their gun-servitors and auto-loaders cycled up to battle readiness. A host of bestial, armoured Skitarii divisions swarmed at the base of the canyon, but Sharaq knew that they would be of little use in any engine fight that might develop.

Only a fraction of the Tempestus Skitarii remained on Mars, but Aeschman, the commander of the Martian divisions, had demanded the right to march out with the engines, and Sharaq wasn't about to deny the towering brute the chance to lead his augmented warriors.

To march out with such a force was almost unheard of on Mars, but with tensions running high in the Tharsis region, Princeps Sharaq was taking no chances with the security of the Legio's fortress.

With Princeps Senioris Cavalerio protecting the reactors of Ipluvien Maximal, Sharaq was next in the chain of command and the security of Ascraeus Mons was his responsibility.

He just wished he had more engines to secure it with.

Two Warhounds and a Reaver fresh from refit was no force to protect an entire base, not when the engines of Mortis were walking.

Cavalerio's battle group was on its way back, but a ferocious dust storm had blown out of the west from the slopes of the Great Mountain to confound the auspex, so, for all intents and purposes, Sharaq was on his own.

Did Mortis have violence in mind? Sharaq didn't know and just hoped this was another of Camulos's posturing walks to demonstrate his Legio's favour on Mars.

'Dolun?' asked Sharaq. 'Where are they?' He didn't need to clarify who he meant.

'Getting engine returns and heat blooms from four or five engines, my princeps,' said his sensori, feeding the information to Sharaq through the Manifold. The view through the cabin windows was a swirling, seething mass of orange and brown dust particles, the smooth-finished rock of the canyon sides barely visible in the gloom.

Sharaq needed no visual cues to command the Metallus Cebrenia, for he was navigating and driving his engine via the sensorium of the Manifold, a much more reliable source of information than the poor sense of his eyes.

'I estimate sixty kilometres out, closing fast,' said Dolun. 'Possible four engines, striding speed or better.'

'Throne, they're big,' hissed Moderati Bannan.

'Warlords,' said Sharaq. 'Three of them. And maybe a Reaver.'

'Probably,' noted Bannan. 'But that heat bloom in the centre… it's too big for one engine. Might be another marching in close formation. They could be trying to hide another engine.'

'Dolun?' queried Sharaq. 'What do you make of that assessment?'

'Could be, but the void returns I'm getting don't look like separate tracks. It's hard to tell, the storms blowing in from the west are messing with every piece of surveyor gear I've got.'

'Keep on it,' ordered Sharaq, flexing his fists in their sheaves of steel and wire. A rumbling thunder vibrated along the great pistons and cogs of Metallus Cebrenia's colossal frame as the god-machine sensed his anticipation through the Manifold. Cebrenia was an old machine, a grand dam of the Legio with an enviable honour roll, but she had faltered in her last battle and taken severe damage.

The journey back to Mars for refit and repair had been difficult for both man and machine, and Sharaq could feel the pressure to perform in this engagement.

'Any word from Mortis?' he demanded. 'Any response to our hails?'

'Negative, my princeps,' replied Bannan. 'I'm just getting static. Could be the storm is playing with the vox, but I doubt it.'

'What about the Stormlord? Any word from Princeps Cavalerio?'

'Last transmission we had said they were heading back at flank speed,' said Bannan. 'Nothing since then.'

'Come on, Indias,' whispered Sharaq. 'I can't hold the Chasmata with a Reaver and two Warhounds.'

He returned his attention to the Manifold, trying to make some sense of the squalls and interference that fogged his perceptions of the world around his engine.

The Martian networks had been jammed for days with scrappy, fragmentary code blurts that appeared to have no point of origin, and which ghosted around the system before vanishing just as inexplicably.

'Adept Eskund, reduce reactor power twelve per cent,' ordered Sharaq. 'Bannan, bring us to one third. Hold us at the mouth of the canyon.'

'Yes, my princeps,' said Bannan, easing down on their speed.

Sharaq opened the Manifold to the princeps of the two Warhounds and said, 'Kasim, Lamnos.'

Ghostly images, rippling and unsteady, formed in the air before Sharaq's eyes: Kasim, the swarthy-skinned predator, and Lamnos, the ambusher who killed from the shadows. Both warriors worked well together, Kasim fighting with the aggression of a hunter to flush prey towards the killing fire of his brother-in-arms.

'Princeps Sharaq,' said Kasim, his voice thick with the accent of the hives of Phoenicus Lacus. 'You have hunting orders?'

'Maybe,' said Sharaq. 'Spread out and run a criss-cross search pattern out towards the last fix we had on Mortis. I want to know where those damned engines are.'

'Are we to engage?' asked Lamnos, and Sharaq almost laughed at the eagerness he heard in his fellow princeps voice.

'Your courage is admirable, Lamnos, but if Mortis are coming in the strength I think they are, a pair of Warhounds won't stop them.'

'Then we just let them march on our fortress unopposed?' demanded Kasim.

'We don't know where they're marching yet,' Sharaq reminded his bellicose Warhound drivers. 'They may swing westwards and carry on north to the Olympica Fossae assembly yards. Or they could bear east towards Mondus Occulum. We don't know.'

'They will rue the day if they cross the Tempest Line,' snarled Lamnos.

'Yes, they will,' agreed Sharaq, 'but until they do and are within our engagement zone, you are not to fire unless fired upon. I won't have Camulos saying we started an engine war on Mars thanks to a headstrong Tempest driver. Understood?'