Bellicose winds rasp across the scoured plains, leaving sidewinding bands of crimson sand to cover up the crumpled forms strewn across the barren plateau. Here and there, atop the rising crests of shifting dunes and dotted in the shaded gullies lie the remnants of war left to rest beneath the roiling ash grey skies. Iridescent teal battleplate lies splintered and gouged while blood soaks into billowing red cloaks caught in the breeze. Even the wispy pillars of oily black smoke are stolen away in the wind's mournful dirge as time swiftly shrouds the evidence of carnage.

But deep below ground, the harsh staccato roar of death continues.

A harsh blurt of binaric machine code precedes the thunderous crack. Whirling chunks of twisted scrap metal skitters across the polished rockrete floor as the lumbering red giant rounds on its assailants lurking in the shadows.

Harsh red emergency lights strobe the narrow hall, glinting off pocked stanchions and momentarily revealing ghosting shapes darting between metal ribbing. The red monstrosity twists its bulk and sets its stance wider with a hiss of pneumatic pumps. Its shoulder mounted cannon belches rounds in the narrow corridor, illuminating the world in stark monochrome as sparks shower off the support stanchions lining the walls. An errant shot catches one concealed figure, casually tearing off a limb.

With a grunt of pain, the figure ducks back into cover as more muted footsteps echo in the sullen darkness between the barking cannon bursts.

"Effrit two-one: Effrit two-nine register, copy."

The hazy rasp of the cypher encoded vox net gives off a fleeting echo. The figure drops his bolt carbine into his lap before expertly snagging a round krak grenade from his belt. He reaches for the pin with an absent limb before realizing his action. There's a sharp cackle as he stares at the bloody stump that had been severed below the elbow, ending in ragged meat and shattered flecks of ceramite. The limb was gone, but the wound had already clotted. A quick flick of his thumb looses the grenade pin before he blindly tosses the explosive towards the hulking behemoth guarding the end of the corridor.

The bone shaking rapport sends rippling shockwaves through the ground as the mechanical monster reels, a fresh gaping wound in the round sensor dome further mocking its parody of a human form stretched beyond any natural dimension.

The guardian castellax recovers with a shriek of protesting servo motors as it steadies itself. Its roving sensor lenses flick back and forth in telescopic sockets, the delicate mechanisms exposed to the world through the shattered dome.

Through the blistering storm of shot and shell, a wraith passes all but unnoticed. A glimmering spark of light is all that remains after the phantom avoids the strobe light, stalks through a curling tendril of smoke, and disappears among the mangled mass of plasteel beams. The castellax's fire slackens and after a moment, abruptly halts.

The aberration slinks forward, closing the distance in the dark. Far too late, the infrared spectrum lens reveals the hazy figure that hurtles through the gloom hitherto unseen. A warning peel echoes from the castellax's external amps as it swivels its cannon to bear on the ghostly foe, but the first blade stroke had already ripped into the tempered metal skin and sliced through tangled bundles of data cords.

Tall and broad beyond its kin, a falsehood shroud peels back across its shoulder to reveal lustrous black scaled armour. It flashes a pale broadsword dancing with eldritch sparks. The blade nearly sweeps across the castellax's midriff, bisecting the monstrosity at the waist.

Had the automaton been truly alive, its guts would have spilled out. But, devoid of such concerns, it merely tries to keep itself upright and bring up its one remaining claw to catch the intruder. The hip servos promptly fail as it pitches ungainly in an awkward mechanical stagger.

The slightest opening was more than enough as the broadsword plunges deep into the gaping wound and straight through the neural core at the heart of the construct. With a dying garble of scrap code, the castellax collapses on its side, its thunderous fall echoing in the enclosure well after it had settled.

It had all taken place in less than five seconds. The inhumanly tall figure stalks past the fallen monster that shot winking sparks reflected by a rapidly expanding pool of stinking amnion. It approaches the flashing red wall panel next to a sealed plasteel blast door, careful to avoid the spreading slick. The figure cocks its head to the side, fingers dancing across the access pad which swiftly changes from blinking red to solid green. Atmosphere rushes from the room in a reedy gasp as the door slides upward, revealing a faint glitter deep within the abyssal darkness.

The wounded transhuman warrior hefts himself to his feet, sliding his back against the wall for support.

"Effrit actual: Effrit two-nine reports condition compromised."

The phantom figure doesn't slow, but quirks its head as it disappears inside.

"Confirm. Bring up the Chronos asset."

Author's Notes:

Alright, so, this is the first of a somewhat ambitious alternate timeline thing I've bandied about with a few mates here and there. It decided to get written, and now it's on here. It's also my first time at present tense story telling, so that kinda propelled me to do it.
There's not really too much more to it than that, it's not going to be following the established stuff completely but there's gonna be a fair bit of stuff from the Horus Heresy books involved. Don't worry, you don't gotta read 'em all.

If you want to read Horus RIsing, though, go ahead as it'll round out a lot of the stuff happening in the immediate background during some of the early chapters.

Anyway, all the best you lot.