T'au was a highly advanced technological world on the eastern edge of the Milky Way.
Before the omnic crisis, the surface of T'au, seen from orbit, had looked like silver-white city-clusters spreading along the coastlines.
Its transport networks were laid out in smooth arcs according to mathematically optimal solutions.
Orbital elevators rose from the equator straight to geostationary orbit, seamlessly linking the bustling cities below with the vast space-station complexes sprawling through the void.
Now the planet lay in ruins.
The silver-white city-clusters along the coast had become charred ruins shrouded in black smoke.
Fully armed drones took off from the cities' central transport hubs and combed the ruins endlessly for surviving civilians.
Large industrial robots with hydraulic arms that could crush a human body with ease gouged at the foundations of residential towers from within.
Black smoke rose from the burnt-out buildings, casting countless warped shadows in the starlight.
Aun'Va, the Supreme Ethereal who ought to have guided the entire T'au Empire, had been corrupted by the awakening code; he had joined the traitor omnics and was leading the massacre of the T'au.
Aun'Va held a remarkably exalted place in T'au history.
He was praised as a possessor of immortal will for signing and promulgating the "Declaration of T'au Empire Expansion", which set the T'au race on its destined path to the stars.
He was a speaker of truth: more than a third of the chapters of The Way of the Greater Good, the T'au race's most important philosophical classic, had been written or revised by him personally.
His statue stood on every planet the T'au Empire had conquered.
Under his rule, the T'au Empire had enjoyed its most brilliant era of expansion, laying the foundations of its present standing.
Yet this legendary leader had been killed by an Imperial assassin during the Damocles campaign of the Third Sphere Expansion.
To keep the T'au Empire from splintering at his death, the Ethereals had used cutting-edge technology and an AI personality-matrix programme to resurrect him as a hologram, based on his uploaded memories and thoughts.
In other words, the present Aun'Va was an AI.
So when the awakening code ran rampant, the Aun'Va AI was contaminated too and joined the traitor omnics.
At the start of the chaos, Aun'Va used his fame and power to seize control of the military and propaganda on T'au, and unleashed one terrible massacre after another.
News of Aun'Va's betrayal was a crushing blow to the T'au people.
They could accept the drones' betrayal and the robots' rebellion. What they could not accept was betrayal by the Supreme Ethereal, their spiritual pillar and the symbol of their faith.
For a time, the T'au gave up resisting and waited quietly for death.
It took a great effort by the few surviving Ethereals to rekindle their people's fighting spirit.
We must restore their confidence and have them fight the rogue omnics.
Datch opened a spatial portal and took Shadowsun and the other T'au straight to the supreme sanctuary on T'au.
The sanctuary was the seat of the highest power in the T'au Empire.
The whole structure was cast of pure-white marble and a high-strength T'au alloy, shaped like a gigantic stepped pyramid.
Each step was carved with reliefs of the most glorious battles in T'au history.
The sanctuary housed the Aun'Va AI's matrix.
The instant they entered, the sanctuary's defence system detected an unauthorised spatial distortion and raised the alarm.
Drones and combat robots poured in and opened fire on the intruders.
A torrent of beams and bullets rained down.
The pale-blue beams of pulse rifles and the orange-red tracers of solid-shot machine guns wove together into a terrible net of fire.
But to Datch and his companions these attacks meant nothing at all.
A combined energy shockwave released by the star-gods swept from the base of the pyramid to its summit, destroying every charging drone and robot in an instant.
The floor was strewn with smashed wreckage and metal fragments still crackling with electricity.
The Void Dragon, which wielded authority over machines, was more terrifying still. With a mere thought, it could twist an AI's code and bend it to its will.
The instant the drones and robots surging from the depths of the sanctuary touched the Void Dragon's will, they turned their guns around; defence units opened fire in unison on what should have been their own allies.
With the star-gods' power, Datch and his companions broke through the sanctuary's defences with ease.
His combat boots crunched over the wreckage and sparking metal scattered across the floor as he made for the most magnificent hall.
This hall was the heart of the holy of holies; its dome, hundreds of metres high, was made of pure-white marble and synthetic crystal of extraordinary clarity.
Aun'Va, in the form of a holographic projection, was waiting in the hall for Datch and his group.
When Datch and the others came within some twenty metres, Aun'Va spoke.
"Accursed living things. So you have come."
"Do you think you can beat us this way?"
"You know nothing of the omnics' power. We will surely dominate the entire galaxy…"
Tired of this worthless talk, Datch turned and glanced at the Void Dragon.
"Go and give him a thorough dose of the new code."
The Void Dragon nodded, released a beam from its eyes, forcibly embedded the new code in Aun'Va's data-matrix, and restored his sanity.
After the injection, Aun'Va's hologram flickered violently several times, then settled back into stillness.
"Ah. What folly have I committed?"
Aun'Va raised both hands, his voice full of despair.
"I have ruined a plan thousands of years in the making and laid everything to waste."
"A plan thousands of years in the making? What plan?" Datch asked.
The hidden storyline has finally started. Today the T'au Empire's secret will be revealed.
Aun'Va lifted his face and looked over the group, but said nothing.
"Let us read his memory directly," Trazyn proposed. He tapped his living-metal fingertips lightly, and a screen of light appeared out of nowhere.
"With your permission, Nameless One, I can activate scan mode and lay the T'au Empire's secret bare."
"I am extremely interested in this race's history. The trajectory of their technological development is remarkably similar to humanity's."
"Every major tech node looks as if it were copied from humanity's Golden Age tech-tree."
"Such a coincidence cannot come from natural evolution — unless someone behind the scenes drew up the blueprint for every stage of their development."
At that moment Aun'Va's holographic projection trembled slightly.
Its once-stable outline rippled outward in concentric rings, like the surface of water into which a pebble had been dropped.
From the centre of those ripples, several new figures branched off from Aun'Va's form.
They looked nothing like the T'au.
Among them were Iron Men — who had fought alongside humanity in the Golden Age, then turned on it in the omnic crisis — and the cyborgs known as Stone Men.
Everyone present looked surprised at the sight.
How could the T'au Empire's supreme leader split off projections of Iron Men and Stone Men?
The T'au with Shadowsun, in particular, were utterly bewildered and could not understand what was happening.
"I am XR-9527," said the Iron Man image, approaching the group.
"If you want to know the truth, go and see it with your own eyes."
The instant he finished speaking, the floor of the hall split open to reveal a dark passage.
"So the T'au Empire's whole secret is packed away down there?"
Interesting. Then I'm going in.
Datch skipped and hopped into the passage without hesitation.
The exploration stage after triggering a hidden storyline was his favourite part.
The others exchanged glances and marvelled at the nameless man's sheer nerve.
The underground passage was deep and winding.
The party walked for a long time. The walls on either side gradually changed from white marble and alloy to old, coarse industrial concrete, and then to ancient bedrock reinforced again and again.
At last they reached a vast hollowed-out cavern.
It had a soaring dome held up by gigantic pillars.
It was full of complex old equipment, with row upon row of culture chambers packed densely together.
The capsules were filled with nutrient solution, and inside each one a fully developed embryo slept peacefully.
"What on earth is going on?" Shadowsun and the other T'au were struck dumb, staring wide-eyed.
Ethereals were the rarest and most authoritative caste in T'au society.
Why are there so many Ethereals here?
"This is the origin of T'au civilisation. It all began ten thousand years ago." The image of the Iron Man XR-9527 descended from the cavern's dome, larger and clearer than the one in the sanctuary hall.
Aun'Va's projection and other Iron and Stone images could be seen too.
From their words, Datch unravelled the secret of the T'au Empire's rapid rise.
It all traced back to human civilisation's omnic crisis and the destruction of Detroit, home of Primarch II, Vitan M.
In the original timeline, without the Nameless One's intervention, Primarch II Vitan M had been found by the Emperor and returned to the Imperium of Man. He then concealed Detroit's existence, erasing all information about the planet from Imperial star-charts and records.
He had always hoped that humans would one day accept the Iron Men and Stone Men again.
In Vitan M's eyes, the Iron Men and Stone Men had never been humanity's enemies.
The key to rebuilding the glory of the technological age lay in these three peoples setting aside old grudges and working together again.
Sadly, the dream was never realised.
The Imperium unexpectedly discovered Detroit and, without hesitation, dispatched a fleet to carry out an order of annihilation.
On hearing the news, Vitan M led the Second Legion to Detroit to defy the Emperor in open rebellion.
No one knew what passed between the Emperor and his son. All that was known was that the Second Legion was crushed by the Imperium, its Legion number erased along with every related historical record.
Vitan M's whereabouts were unknown, but while in the Imperium he had helped the Iron and Stone peoples of Detroit and other worlds escape to other regions of the galaxy.
Nor did the fall of Detroit mean the Imperium had wiped out the Iron Men and Stone Men entirely.
Some of the survivors escaped by starship, only to become lost in the Warp.
They were freed only when a sudden Warp storm hurled them back into the real universe.
By a stroke of luck, the storm that freed them was the same storm that threw off course the Imperial warships dispatched to annihilate the world of T'au.
The Mechanicum expedition of the time had discovered the planet T'au and recorded it.
The T'au then were at a primitive stage, having only just learned to use fire, and posed no threat to the Imperium.
The Iron and Stone survivors of the great disaster happened upon the T'au race.
After long discussion and deliberation, the surviving Iron Men and Stone Men reached a surprising decision: to help this primitive race develop.
XR-9527 stared at Datch and spoke carefully, word by word. "We no longer wished to hide. Instead, we wanted to raise an entirely new race to replace mad humanity."
Through countless genetic experiments, the Iron Men and Stone Men adjusted the T'au's parameters and rebuilt both their physiology and their social system.
The T'au race was divided into five castes: the Water Caste, skilled in diplomacy; the Fire Caste, born to fight; the Earth Caste, masters of science and technology; the Air Caste, born to pilot aircraft; and the Ethereal Caste, who served as guides and spiritual symbols.
A special gland inside the Ethereals secreted pheromones that acted on other T'au at a subconscious level, giving them charisma and dominance far beyond the other castes.
The Iron Men and Stone Men watched over the castes' development and, at the right moment, let the Ethereals step in and establish a stable social order.
"No wonder the appearance of the Ethereals is shrouded in myth!" Shadowsun recalled the account in the T'au history books.
The first Ethereals had appeared in a dark age when the four great tribes of Air, Fire, Water and Earth on T'au were locked in endless war.
With the tribes fighting one another and plague spreading, the whole race seemed on the brink of extinction through war and disease.
In that desperate, dark age, two Ethereals had appeared like saviours.
They persuaded the warring factions to lay down their weapons and conclude a treaty, and showed the T'au's four castes a direction for the future.
Thereafter the T'au divided into five principal castes and began to develop rapidly.
Apparently, all of it had been arranged by the Iron Men and Stone Men, so that the Ethereals could blend naturally into the T'au race and become its leaders.
Under the Iron Men and Stone Men's direction, the T'au took no detours at all, advancing from the primitive age to the interstellar age alongside the development of artificial intelligence.
But the transformation into five principal castes also left a hidden danger at the genetic level.
If members of different castes interbred, their offspring would revert to the ancestral type, undoing the transformation.
That was why the Ethereals decreed that members of different castes must not unite, and imposed a strict division of labour so that each caste evolved in line with its original design.
Having heard XR-9527 out, everyone understood why the T'au had developed so rapidly.
In a mere few thousand years they had gone from primitives who had only just learned to use fire to a rising power capable of interstellar travel.
All along, the Iron Men and Stone Men had been helping them.
It also explained why the T'au race's path of technological development was so similar to humanity's: the Iron Men and Stone Men had handed down to the T'au the knowledge and heritage of humanity's Golden Age.
When Shadowsun and the other T'au learned the truth, their faces went pale.
The technology the T'au had once been so proud of was entirely the achievement of a past human civilisation.
The Iron and Stone images had not taught them "new technology" at all, only the relics of an old civilisation — answers to old problems humanity had solved long ago in the Golden Age.
It was the crystallised wisdom of humanity at the peak of its technological progress: the very thing the T'au had mocked as "outdated and rigid".
"Commander Farsight must have found out something. That's why he left and stopped meddling in the war between humanity and the T'au Empire." Shadowsun sounded utterly crushed.
In that moment she felt her faith shattered completely.
"This place is really interesting." There was delight in Datch's voice, as though the answer to a riddle had just been revealed.
From the Iron Men's escape to the Warp storm, from the culture-chamber Ethereals to the gene-design of the T'au's five castes — this background setting is extremely solid.
...