With Mars under attack from an unknown foe, it was time to gather one's friends close.

Kane respected Zeth, for she reminded him of a younger version of himself, an adept unafraid to push the boundaries of the known. To Kane, Zeth represented all that was good about the Mechanicum, an adept who possessed a proper reverence for the past and what earlier pioneers had developed that meshed with an unashamed hunger to build upon that knowledge to reach still greater heights.

An ancient alchemist and scientist of Terra had once said that he had seen further by standing on the shoulders of giants. That perfectly applied to Adept Zeth, and Kane knew that if anyone was going to advance the cause of science and reason in the Imperium it was her.

Emboldened by that thought, Kane watched as huge, tracked haulers lifted sealed containers of Astartes weapons and armour for transport to the orbital elevators of Uranius Patera.

'Come, Lachine,' he said. 'Even during a crisis, the work of Mondus Occulum must continue.'

Grey dust, like ashen bone, billowed around the legs of the two Knights as they loped along the edges of the Aganippe Fossae, the long trench that carved into the plains west of the towering form of Arsia Mons.

Leopold Cronus led the way in Pax Mortis, with Raf Maven following behind in the newly repaired Equitos Bellum. Cronus set a brisk striding pace, and Maven had to work hard to keep up with him, for Equitos Bellum was skittish, its controls tight, and the Manifold willfully resisted him at every turn.

It knows the thing that hurt it is still out there, thought Maven, angling his course to follow Cronus and the deep canyon. Dust clouds obscured the view from his cockpit, but there was little to see in this region and he was piloting via the Manifold anyway. The toxic deserts of the pallidus stretched out to the west and south, and the northern sub-hives between here and Ipluvien Maximal's forge were little more than black smudges of hanging smoke and fear to the north.

The Knights followed the course of the chasm towards the Median Bridge, a section of collapsed rock where they could cross before turning eastwards towards their chapter house within the Arsia Chasmata.

'How's it doing?' asked Cronus over the vox-link.

'It's hard work,' admitted Maven. 'It keeps pulling at the controls, but there's no sense to it. Each time I compensate, it returns on the opposite side a moment later.'

'It will take time to readjust,' said Cronus. 'The entire link assembly had to be rebuilt.'

'I know, but it feels stronger than that.'

'Stronger how? What do you mean?'

'Like it's trying to guide me,' said Maven, at a loss how else to explain it. 'Guide you? To where?'

'I don't know, but it's like… like something's pulling at me too.'

Maven heard Cronus sigh over the vox and wished he had something more solid to offer his friend by way of an explanation. All he had was a gut feeling and the firmly-held conviction that his mount knew better than he what needed to be done.

Their deployment had begun three days ago, when they left the chapter house in a fanfare of cheers, squires' trumpets, blaring warhorns and waving cobalt banners. Equitos Bellum marched out, and the brothers of the Knights of Taranis had come to watch it walk once more. For a mount to have returned from the verge of destruction was no small matter and the occasion had to be marked.

Like most of the warrior orders of Tharsis, the Knights of Taranis had been on high alert since the chaos that had engulfed Mars began. Thanks to the noospheric links installed by Adept Zeth, the halls of Taranis had not suffered as horrifically as many others had, though the enginseers had been forced to order an emergency shutdown of the chapter house's main reactor after a fragment of scrapcode attempted to disengage its coolant protocols.

That speedy response had saved the Order of Taranis from a nuclear holocaust, but until the code-scrubbers could purge the corrupted systems, those Knight machines without full power cells would not be able to recharge.

Nor had that been the worst of the damage. Much to Lord Verticorda's anguish, the data looms of the order's librarium had been corrupted beyond repair, taking with them a roll of honour and battle stretching back a thousand years and more.

At the request of Adept Zeth, Lords Caturix and Verticorda had ordered the Knights of Taranis to ride from their chapter house in defence of Mars and the Magma City. Rumour had it that Zeth had also despatched emissaries to Lord Cavalerio of Tempestus to petition their engines to walk, but no one knew what answer she had received.

With several machines powerless to ride until the reactor was repaired, the Knights of Taranis were forced to operate in teams of two instead of three to cover the scale of their deployment. Old Stator had marched out alongside Brother Gentran, a rider newly-elevated from the Errantry, and Maven had been surprised to find that he missed the flinty presence of his preceptor.

Maven and Cronus had ridden east, following a patrol circuit that carried them clockwise around the rumpled skirts of the ancient volcano, before turning to follow the line of the Oti Fossae southwards. As night fell on the second day of their ride, they turned west towards the Magma City to refuel and recharge before continuing on their patrol circuit.

The forge of Koriel Zeth never failed to amaze Maven, glowing like an ember in the distance while the skies above seethed with orange light as though the clouds themselves were afire. Riding closer, lava-filled aqueducts had shone like threads of gold as they carried molten rock from the top of Aetna's Dam, the monolithic structure that formed the entirety of the volcano's southern flank, to the magma lagoon surrounding the city.

Towering walls of ceramite and adamantium ringed the enormous city, and the light of the planet's lifeblood dispelled the darkness as the Knights marched along the mighty, statue-lined Typhon Causeway towards the Vulkan Gate.

Silver and black spires jutted over the walls like metallic teeth, and only after convoluted binaric interrogation by the gate's defences had they been allowed inside. They had stayed within the circuit of the walls just long enough for their mounts' power cells to be brought back to maximum charge before riding out.

The two Knights had continued on their patrol circuit of the enormous volcano, skirting the Magma City's port facilities where millions of tonnes of war materiel was ferried into the hungry bellies of mass-conveyers hanging low in the crowded skies. No sooner had they left the smoking grandeur of Zeth's city than Maven had felt Equitos Bellum pulling at him, an insistent urge that nagged at his hindbrain and sent painful skewers of pain into his mind whenever he resisted.

With their course soon to carry them eastwards towards home, the pull was getting stronger, and Maven gripped the controls tighter as he felt a building ache behind his eyes. He felt every one of his hard-plugs scratching with irritation, as though Equitos Bellum was trying to dislodge him like a wild colt.

'What's the matter with you?' he hissed.

As if in answer, a ghostly flare on the auspex spiked to the south, and Maven flinched as a surge of recognition pulsed in his mind. The image vanished almost as soon as it appeared and he wasn't even sure he'd seen it, but for the briefest instant it had looked like a dreadfully familiar spider-like pattern of electromagnetic energy.

Maven drew his mount to a halt, feeling the pain behind his eyes ease as he did so. The tall machine's hydraulics hissed as it sank down onto its haunches.

'Cronus, wait!' he called, rotating the Knight's upper body with a deft movement of the controls. There was nothing to see here, just bone white ash and dust whipped in from the southern pallidus. He heard the relaxing groan of metal as Equitos Bellum settled, feeling the tension in its limbs and the restless hunger for vengeance burning in its core.