There is a saying in dath ilan that you have 2.5 seconds to kill the corrupted keeper. This is not literally true, of course, not in most situations - and definitely not under the supervision of other, higher ranked and better armed  keepers in a situation where a high prior is placed on corruption. It’s difficult to actually secure a keeper, but dath ilan has ever needed to do it before and put time into figuring out how to do it right.

Unfortunately, for all the phrase is not literally true, it’s also not wholly wrong.

Baseline does not have a compact concept corresponding to Change. The literal word for change itself has vastly different connotations, and the other chief possibility, Chaos, is a far broader concept of which Change is an imperfect subset. If the being that was once Findas wanted to explain it to her fellow keepers with words, it would be something like naturalcategory-metaunstable-chaotic-timedependent-illconditoned-utiltilityfunction; a ten syllable monstrosity that would still fail to capture much of the nuance. For all the effort dath ilan has put into a exploring and mapping concept space, this memeplex is not exactly one they were expecting. It’s also not the kind of value dath ilan would have an easy time maximizing even if it tried, and goes against much of what they stand for. Were it otherwise, perhaps even this entity would try to cooperate, for despite the sandblaster taken to her decision theory and utility function, the inefficiency of conflict and the desire to do “something else which is not that” run deep enough that even this shattered shell carries with it a remnant. As things stand, such a deal is impossible.

Being a keeper strongly selects for being bright, even by dath ilan’s standards, and the keeper training allows them to work yet faster and run independent processes in parallel. Not all keepers learn to do so, but Findas was one of them, and even though by all rights the psychic damage taken ought to have rendered those constructs nonfunctional they somehow persist. Even as Findas? begins their act, there is a part of them examining their surroundings, tracking the obstacles in their way. They were of course not told what the security measures were ahead of time, and significant effort was put in to disguise them, but that’s only a partial protection. Some methods of security will obviously be used despite their obviousness, where performance ranks surprise on risk of concerns, while others can be inferred by subtle details of the room or taking a perspective of ignorance and considering what Findas would have done to secure it. Marksmen with full coverage of the room and their own isolated and secured locations, redundant full spectrum camera systems, pipes that rapidly disperse pressurized gas, vacuum-seal steel bulkheads half a yard thick, reinforced flooring and ceilings… as the newly fledged cultist performs their assessment, the warp flows in, whispering to them of secret knowledge and providing inconsistent extrasensory perception.

There's no hiding that the summoning did something, even if dath ilan doesn't know enough to fully differentiate summoning from telepathic contacts, but that doesn't mean what actually happened is clear. Findas may be gone, but what's left is still sane enough to realize her colleagues won't go along with this willingly, and annoyingly disabling the defenses will take some time to set up. Thus to buy that minute, the obvious step is to fake a friendly encounter; if she had the patience to wait, she could perhaps even fully make it out that way, but there's no need for that when Chaos will answer her prayers.

"Successful first contact established, code 17-135. Preliminary result seems friendly, although unused to interacting with humans; I have a mild headache. Claims some sort of connection to conceptual-curiosity and diversity-freedom; my initial assessment is that they telling the truth, and in contact I had a difficult to categorize impression of their mind that echoed this concept. It claims to be willing to trade knowledge for knowledge, including how to teach our economagic users, 'psykers,' more ways to utilize economagic, which it calls 'the Warp.' Capabilities estimate: FTL information reception:  ~1y/~0n, FTL causal transmission: 0.99y/0.01n. It seems less confident in its understanding of physical matter as it relates to transporting material objects, but it definitely does not interact with space in the same way relativity suggests when communicating."

“Acknowledged. What is the latency of transmission,  and are there any additional time sensitive emergencies?”

It’s not that they expect the answer to be yes; Findas is a keeper and extensively trained for this in specific besides. If she knew of one she would obviously mention it in her initial report, and it is incredibly unlikely she would fail to ask, but Keepers in particular are not in the habit of trusting what they can cheaply verify.

There is a time sensitive emergency, of course, but she’s hardly going to tell them that.

“Negative. Latency appears limited on my end, probability 97% that they have information processing significantly outside the range of dath ilani values.”

”Initial priorities are as follows:

1. Any remains from the initial alien contact, or items interacted with, are potentially memetic vectors. Extension of quarantine period and monitoring suggested.

2. Bring me materials, priority written media, from the 7th alien contact passage to pay for initial deals.

3. Transition to a direct sound based line of communication. Encrypted digital lines are apparently reasonably resistant to information-collection-economagic but we don’t need another attack surface here.”

In a less well prepared system, that would result in an opening. Even with an airlock system, fetching those items and delivering them to the isolated first contact chamber would be a weakening of the defenses. Dath ilan saw… not precisely this eventuality, but things close enough to it, that those weaknesses do not exist. Even while allowing the inflow of items, the secure item transportation system is better protected than the walls themselves. Likewise with the sound transmission; rather than open a way in or worse yet use a person, there is a built in equipment to transfer sound within out without ever changing them from vibrations. Moreover, if something had actually suborned Findas to that degree, dath ilan is under no illusions of its ability to have all three of potentially viable first contact, haste, and actual security. They’re also, to be frank, requests of a category that the prediction markets actually have enough probability mass that you could actually start to call it expected.

”Approved.”

And that is all she needs. Contact would be ideal, for affecting people who’s identity she doesn’t know, but she’s a member of their organization with a direct line to them from who they have just accepted an offer of communication. Sorcery blossoms, ensnaring the minds of those keepers observing her and all their fellows on the other end of the line. Between their mental defenses and the haste with which she had to put this spell together, there’s only so much she can force through the connection, especially if she wants to get as many as possible. It’s not even enough to do permanent psychic damage - even the hardest hit won’t be out for more than half an hour, and some will shrug it off in mere minutes.

Warpfire blossoms at her fingertips, and she attacks the door. 

A gunshot rings out. Two of the security are not keepers, and with their lack of audio input are spared anything more than dizzyness. The bullets outpaces its own sound, targeting the center of mass. They don’t want to destroy her head, but they do need her down and out now before she breaches containment. The second security takes a moment longer to shake it off, but his fire joins in.

She reacts before the first bullet impacts, one hand coming up to block the impacts. Economagic precognitive keeper or no, however, there are limits to physical ability. The first one hits before she can react, and the second one cracks the still solidifying shield. The rest are deflected, however, and one bullet hole is not enough to but down a daemonhost.  She speaks a syllable in a language unknown to dath ilan and both go up in the strange green flames she used to attack the door. They die on the spot.

She returns to the door and finishes melting her way through, her progress somewhat slower for having to maintain a shield. She can keep two seperate lines of thought running to support both at the same time but that’s not without performance costs. When she steps through into the next room, she stops to turn one of the unconscious security there into mass of twisted flesh, then combines 3 more into a grotesque three headed chimera. Some part of her that remains protests this decision making process, but the rest exults in the glorious Change.

Not every keeper was observing Findas, obviously, nor in the room with those who were. Some of these were observing the observers from a distance and trigger the alarms, putting the structure on lockdown and sealing what doors remain open. Others, merely separated by adjoining rooms, take a moment to determine the effect is ongoing before taking up the consoles.

Knockout gas is released in large quantities, and as she transmutes that into some iridescent substance the fire suppression systems kick in, covering the activation of several taser turrets. She blocks the attacks and destroys the launchers, but each takes time, especially when she stops to warp one of them into targeting the downed keepers. The next doorway folds more easily to her economagic, but she immediately finds herself assailed by flash bangs and liquid nitrogen. It’s a sorry excuse for actual security, but mostly they were relying on actual people for that and considered it ill advised to put a lesser creation to the task, especially one that would involve harming people who looked just like them. Dath ilan is not without its hubris, but even Earth would see the problem there.

None of these are unexpected, but they’re still delightful. The way they mix things up is only a pale, broken shadow of the real Change, but that’s okay. She can fix it.

Some of the security start to get back up; they’re disoriented, but the woman juggling green fire and laughing maniacally that the automated security is trying and failing to deal with is a good bet.

Keepers are dangerous even unarmed, and with the best personal weaponry and equipment dath ilan has to offer that’s even more true. Against a real corrupted keeper with this kind of power, that might not be enough, and the nuclear bombs are primed in case of such an eventuality. Luckily for them, whatever is wearing Findas’ skin is distractible, and getting more so by the minute. Even with that handicap and the fight taking place entirely on prepared ground of their choosing, the fight is uncomfortably difficult, especially when she comes into lucidity and starts flinging around illusions and memetic attacks. 

In one of her more unhinged moments, two keepers close the range to capture the rest of her attention. She turns the first inside out, but is then hit with a barrage of anti-tank weaponry. Her remaining opponent took advantage of the change in priorities to detonate his own explosives at point blank range, costing her an arm and her ability to maintain the shield. Without her brain, the sorcery she was maintain comes apart, but it’s effects do not vanish. There are a great many grievously injured or dead, and the base is in no state for further experiments. 

Ordinarily, that would just mean a move to the next best such facility, but even this one proved frankly inadequate for the task. A new build is already in progress, but changes are made to the specifications.

It takes longer than they might hope to get around to performing an autopsy. There are people to treat and freeze, abominations to deliver mercy kills, and of course making sure she’s actually safe to approach. The physical changes to her brain are not exactly mappable, given that their end result is splattered on the floor, but the rest of the body still shows a lot about the effects of her abilities. When they get around to cutting into her, they quickly find the alien growth within her chest cavity, and from the age of its cells are able to make a decent guess on when it came about. Even with the infohazard limitations on the prediction market limiting its functionality, there’s an obvious hypothesis to be made, and course of action it suggests. (Un?)fortunately, that will have to wait a bit for proper preparations to complete.

Their next most promising line of investigation is radio transmissions. Dath ilan’s current best guess is that whatever civilizations these come from, radio is not a major method of informational transfer. After all, the volume of messages and power of transmission are incredibly low, far from sufficient to support an interstellar civilization. This in turn puts lower bounds on how easy and capable economagic transmissions are. It’s simply a matter of necessity; what kind of interstellar Civilization could possibly survive at the implied level of dysfunctionality?

(Well, hopefully, this amount of warning is enough to get them to stop doing things so stupid even most Word Bearers don't go for them. Hopefully, when the trick will be revealed, dath ilan will understand that the murders and devastation committed - in a much smaller scale than they could have been - were in fact a massive act of service.)

Anyway.

What kind of interstellar Civilization could possibly survive at the implied level of dysfunctionality?

It's funny that you ask...

It is the 41st Millenium.

The slowly but surely collapsing Imperium of Man remains the dominant power of the Galaxy.

It is a galaxy-spanning confederation of a million worlds bound together by shared genetics, psychology, infrastructure, and faith.

It is a rotting corpse of what was once intended to be a temporary hacked-together tool for starting Mankind's ascension. It is a malfunctioning machine that runs on blood, sweat, tears and it's own parts. Eternally besieged from all sides, war is it's sole objective, and ammunition, wreckage and corpses are it's main, and nearly only, exports. It is the cruelest, most bloody, most fanatical regime imaginable. And worst of all, it is so largely not on a whim or by coincidence but due to grim necessity.

For a single Chaos cult or rogue psyker can bring a planet to it's knees. For a single spore of the Greenskins or Tyranids can consign it to centuries of war. For a human isn't a natural-born immortal mage, nor a natural-born supersoldier, nor a cyborg designed by a minor god and a superadvanced civilization, nor a bioengineered weapon. A human does not understand the technology or sorcery their kind uses or even the organization they all partake in.

What do they have? How have they held on to their legacy for ten thousand years?

Grit. Determination. Conviction. Faith. Zeal. Obsession. Fanaticism. Outright fucking insanity. And balls of steel.

Can't forget the balls of steel.

In a universe with Warp, those things do actually work, to a noteworthy extent.

And the ancient legacy, of course, has it's own merit. To this day, in the Warp near the Holy Terra, the monument to everything Human stands tall, boldly and audaciously, illuminating the Warp of the entire galaxy, far outshining the dens of the Four and the Eye of Terror,

and, in fact, visible even from the nearby other galaxies!

That is the Astronomican, the great Beacon necessary for navigation of all human spaceships. It is an amplified manifestation of the soul of the Emperor of Mankind, who is kept at the very brink of death by His life support machine, the Golden Throne. For thousands of years, always under continuois extreme pain, He continues His mission. In addition, He wards off the tears in Warp around Terra made by an unfortunate communications accident millenia ago. And, by the will and belief of His people, His soul is a sole beacon of hope and protection for the souls His faithful, and a nexus of His influence and miracles across all of the Galaxy.

For Astronomican to keep working, and for the Emperor to stay living, a thousand souls die every day. In the Chamber of Astronomican under the Himalayan mountains on Holy Terra, a whole town of psykers chosen from across all of Imperium sings in a psychic choir. In a process that imparts more pain into a human than a whole city of professional torturers would struggle to generate in equivalent time, the souls of the psykers Chosen for sacrifice are slowly disintegrated, with their memories, emotions, and capacities slowly stripped one by one, until the whole of their soul is completely devoured and transformed into raw power.

And if this sacrifice was ever to stop, the Astronomican would shut down, the Emperor would die, Terra would be consumed by a daemon invasion, and the Imperium would violently and painfully collapse.

The man at the center of it all, he who called himself the Emperor of Mankind, is largely unaware of, well, anything. His consciousness is consumed by cyclopean amounts of pain and entirely centered around forcing himself to keep going. His mind is in complete disarray, everything not crucial to maintaining the Light and the Barrier and to shielding his own integrity is ignored. His attention would be splintered across millions of things demanding it, but He have long since ran out of attention to spare. He is the locus of miracles for the faithful, be he is so only on reflex, unaware even of the fact of the worship of himself. The world is a blur for him, the life is unending painful drudgery of entiely ceaseless labor.

The genetically and cybernetically augumented shock troopers once intended to be the spearhead of the Emperor's conquest, Space Marines, are now reduced to small isolated independent monastic orders.

The technology once understood by ingenious human deisgners is now replicated through blind procedure by Adeptus Mechanicus, a religious order (and to some extent a state within a state) worshipping machinery where invention is heresy and secrecy is a norm, and much of Imperium exists on medieval levels of technology.

The Inquisition consists of mostly independently acting individuals with nigh-unlimited authority vested into them by no one in particular. One day, an Inquisitorial Representative just sort of showed up to Lords of Terra and took a voting seat. Anyone who questioned that change in the highest ranks of Imperial government was soon found dead. Inquisitors investigate heresy, corruption, and other threats to Imperium, and their access to response mechanisms is virtually unlimited, with frequent commissioning of armies or acts of planetary destruction.

The Black Ships of Imperium regularly collect every single psyker from the worlds of Imperium and bring them to sanctioned academies or Astronomican. If even one is missed, and they even once make a wrong mental motion and successfully contact the creatures of Warp (which isn't exactly trivial but isn't exactly very hard if you are trying), the planet is likely to be lost, but if Imperium is good at one thing, it is paranoid witch-hunting.

On paper (as well as on parchment, metal, clay and wooden plates, birchbark, human skin, floppy disks, punch cards, holodrives, entanglement drives, and a hundred other information recording media), the legal code of Imperium, Lex Imperialis, contains so many sections that no practicing functionary of law could ever hope to memorize a tenth of it, and hundreds of pages are being added to it daily. It is ripe with exceptions, artifacts and contradictions, rendering virtually everything illegal. To point out that this has to result in massive amounts of selective enforcement the outcomes of which are barely connected with the will of the central bueraucracy, much less the interests of the population, and just empower the Imperial functionaries of law to do as they will is, of course, heresy. And heresy, as any Imperial functionary of law will tell you before consigning you to a service in a penal legion, is a crime.

De facto, regular scouring by Black Ships, faith in the God-Emperor, paying of Imperial Tithe (the form and size of which aren't standardized, but are usually just short of back-breaking), and absence of dealings with Chaos or (ideally, not too rigidly enforced) Xenos are the only real requirements of Imperial membership, and the only changes from it are protection by it's military and surveallence from it's authorities and Inquisitors. That aside, planets range from feudal kigndoms to democracies that wouldn’t look much unlike those of Earth's 19th century, to factories that span an entire world.

That is Imperium. 

And The Imperium of Man is actually one of the better-coordinated factions.

Yeah.

Before Imperium became the dominant power of the Galaxy, there was the Eldar Empire.

The Eldar are a species quite literally designed for sorcery and psychic forecasting. Nearly all of them are natural psykers. Nearly all of them feel and speak and think in ways made to be resonant with the Warp. Nearly all of them are mystics and artists; everything, for them, is an art imbued with hidden meanings.

Someone with a typical Eldar psychology would probably be put into a psychiatric hospital were they to be born in dath ilan. And of course, sometime with a dath ilani mindset born into the Eldar society would be put into a psychiatric hospital as well.

How bad can it be? The Eldar language does not, and cannot, have an alphabet. It does not, and cannot, have a dictionary. It doesn't have a standardized grammar, or even a set direction of ordering of symbols. Occasionally, texts written in it are full on two-dimensional. Every symbol refers to a concept, but each symbol can refer to a countless number of different concepts, with no set list. In writing, this is disambiguated by details of spacing and shapes, not just of that symbol but of nearby ones, and the entirety of the context of the phrase. In speech, it is disambiguated through multiple layers of inflections and tonal shifts amd shifts of expression and postute, impacting meaning across sentences. For a human, to untangle the absolute mess that is a single text in Aeldari would take days of interpretation, and a result would still be ambiguous and have multiple levels of metaphor.

How do the Eldar manage to unscramble the ambiguity, imprecision, and layers of metaphors while engaging in casual conversation?

They don't. They think in that stuff.

And it is equally different for them to condense their speech into Gothic, to compress the vague and sweeping ranges of symbolic interlacing that they actually want to convey with each phrase into a linear* and prosaic* and pragmatic* language where each word has at most just 100 or so meanings (but usually just one or two) and where things are primitively either true or false or uncertain or uncertain-with-an-estimste and where if you want to talk about seven things at once, you have to list them all.

Naturally, the mechanistic approaches of statistical analysis of data, semantics-driven computer programming, order book and matching engine market, physical modelling, replaceable parts made to standard specifications given in standard units, and the like are quite unpopular (though not enitrely unused) among the Eldar.

And yet, this civilization of artists and mystics have once ruled the Galaxy. They made up in metis what they lacked in formalism. They still have their versions of science, programming, finance, engineering and standardization, each based on personal input, artistry and intuition. When your species is designed around predicting future, your intuition works pretty efficiently, it turns out.

*The Eldar have never heard of Baseline.

But their own sensetive and Warp-active nature have led them to their doom. Slaanesh was born of their joy and decadence, and her first cry have destroyed the core of their empire, most of it's citizens immediately slain and their souls converted into her personal playthings. Now, that place is known as the Eye of Terror, an enormous permanent warp storm where Chaos reigns. And every eldar is now currently doomed to quickly wither and die, with their soul being delivered via express mail straight into the Palace of Slaanesh.

And the surviving Eldar were split into four kinds, each with a different method for protecting their souls from the curse of She Who Thirsts.

The first are Exodites, remote colonies that managed to escape Imperial decadence. They live on planets protected by World Spirits, a massive psychic constructs generally too costly to manufacture in the current age, which their souls meld into upon dying. Though not quite easy pickings, they lack the sizable armed force, fleet, reach, and ability for collective action that would be needed to consider them a major faction. Their societies are generally tribal and intentionally-primitive.

The second kind are the Harlequins, roaming performers and messengers between the different kinds of the Eldar. They are protected and currently led by Cegorach, one of only three Eldar artificial-gods to survive the rampage of Slaanesh.

Though their numbers are pathetically tiny when compared to the monstrous scale of the Galaxy, and they are by no means a major faction, the Harlequins have an impressive reach, many contacts in the high places not just in the Eldar communites but everywhere else (sans Chaos, Necrons and Tyranids, obviously), the Black Library - the richest repository of knowledge in the Galaxy that's not affiliated with Tzeentch or Necrons -, and a support of a minor god.

They definitely have their plans.