The Empty Synod looks around at the Imperium, at the galaxy, at its brutality and cruelty and waste and stupidity, and says "None of this is necessary. Everything could different. We can make it so." It embodies the forces of hope in a universe otherwise bereft of it.
What Does the Empty Synod Want?
The Empty Synod wants to overthrow the Imperium and replace it with a more just and effective society. It wants to liberate all the mutants and psykers from Imperial oppression and turn their talents to the benefits of all. It wants to genetically engineer and cognitive condition humanity to incorporate the best aspects of xenos and alternate forms of humanity while leaving behind its worst traits. It wants peace with all xenos where it is possible, and to incorporate their technology, insights, and worldviews into a greater galactic society. It wants to restart technological progress and unleash the power of artificial intelligences, human cognitive development, and cybernetic augmentation to exceed the height of humanity's powers during the Age of Technology. It wants to develop the human race's capacities to the point where it can ascend psychically en masse, master the warp, and challenge the gods.
The Empty Synod works on projects designed to further all of these goals, but its primary focus is on the overthrow of Imperial, Ecclesiarchical, and Mechanicus authorities in order to sweep away the forces that are mostly able to interfere with the rest of its agenda. Despite standing against the Ecclesiarchy, the Empty Synod avoids taking an official position on the deification of the Emperor, and it is not against leveraging the power of religious belief in its favour.
Who Are They?
The leaders of the Empty Synod are known only by the collective title of the Eisholoi, "Those who move into wholeness" in High Gothic. Many are or were human, but some never were. Some may never even have lived. They are never seen in person. They can communicate with their key agents through mysterious, impossible means, and they muster strange and unknown powers to see their will is done.
Under them are the Epistatai (sing. Epistates) and Taxiarchs, the senior divisional leaders of the organisation. The Epistatai are usually embedded within the Adepta Terra or in remote locations within the Halo Stars. They lead research projects, divert Imperial resources and powers to the service of the Empty Synod, and collect intelligence to pass on. Taxiarchs are given broad geographic areas (usually at least one entire system) in which they are expected to undermine and attack the Imperium. These are the only ranks who communicate directly with the Eisholoi.
Each Taxiarch and Epistates is served by teams of agents who execute operations on their behalf, with the key division being those who know they work for for the Empty Synod (the minority) and those who do not. The former are known as "Hetaroi" ("Companions") while the latter are known as "Pseudophores" ("Lie-carriers") or simply as "assets".
So What's the Plan?
The Noctis Aeterna has catalysed the Empty Synod into activating its Taxiarchs in the Cinders and the Wisp. With the severe degradation of the astropathic network and interstellar trade, there is a unique opportunity to break planets and systems off from the Imperium and use them as bases for future expansion. The Empty Synod has been expanding its control of Chartist shipping aggressively, trying to monopolize interstellar shipping in the Cinders so that when a few key systems fall to their influence, the rest will be forced to join up or be deprived of essential resources and the capacity to defend themselves.
Exploring the Webway: Many of the worlds of the Tellian sector had or have active gates to the Webway, the ancient Aeldari network for superluminal travel. The Empty Synod seeks to discover the locations of these gates, as well as the means to activate them, in order to use them for their own ends, both to circumvent eventual Imperial blockades, as well as to evacuate the populations of planets they will eventually control should the Imperium try to exterminate them. To aid with this, the Empty Synod actively seeks out items and sites of cultural or strategic importance to the Eldar, and returns them in exchange for knowledge of the Webway and the xenos' permission to use it.
Technical Power: Archaeotech, xenotech, heretek, the Tellian sector is rich in all three, and the Empty Synod wants to discover and control as much of it as possible. They actively have teams scouting out old Varosi and other ancient sites; negotiating with Rogue Traders and xenos; and researching new avenues of development. They are particularly interested in technology that could fundamentally transform the balance of power between them and the Imperium.
Solomar Holdings: Solomar Holdings is one of several front groups the Empty Synod has created in order to create the financial support they require, while inserting themselves into the vital arteries of the Imperium. Solomar is notionally a confederation of Chartist Captains (most have no idea they work for the Empty Synod) who trade across two dozen systems in the Cinders, with a focus on bulk staples (promethium, food, metals), weapons, and vehicles. While most other Chartist fleets have seen significant degradation of their transit capabilities since the end of the Astronomican, Solomar has not, and it has been using this advantage to aggressively grow. Its main rival across most of the Cinders is the Pratik Fleet, a Rogue Trader dynasty that is highly corrupt and unorthodox, but only in pursuit of its own power and wealth.
Mutant Militias: The Empty Synod seeks to recruit, train, and arm extensive military forces from mutants, underhivers, heretical cults, and other outcastes in order to challenge the Imperium's military might. These groups are rarely under the direct control of Taxiarchs, but are supported and steered away from falling under the control of Chaos outright.
Allies and Enemies
Chaos: The Empty Synod is not opposed to Chaos per se, but it sees it as simply the obverse side of the Imperium, each cultivating and reacting to the worst tendencies in the other. It discourages, but does not prevent, its operatives from drawing on Chaotic powers, and it periodically temporarily aligns with Chaotic movements but does not incorporate them into itself. The two Chaos-aligned groups the Empty Synod deals with regularly are the Black Dawn, a Nurgle cult, and the Joyous Ascent, a rogue psychic ascendance cult, but it is as likely to be fighting both groups as working with them.
Xenos: The two most common xenos for the Empty Synod to deal with are the Mzod and the Aeldari, and it is widely believed that representatives of both species sit on the Eisholoi. The Empty Synod primarily deals with non-Craftworld Eldar, either Exodites who dwell on Maiden Worlds or the groups that continually inhabit the Webway itself. The Empty Synod studies Orks, and has occasionally considered weaponising them, but considers it too probable that they will escape control. It has occasional, often profitable, exchange with another two dozen more obscure species out amongst the Halo Stars. The Empty Synod is attempting to initiate contact with the Zul-Kan, but this has been unsuccessful so far.
Heretical Cults: The Empty Synod supports and encourages deviant versions of the Imperial Creed, especially versions that soften the anti-mutant, psyker, and xenos positions associated with the baseline doctrine. It recruits extensively from such cults, and often provides them with secret support to help them undermine the Ecclesiarchy.
The Adeptus Mechanicus: There is a vibrant, if secretive, backdoor trade of technical artifacts with the Adeptus Mechanicus through various front groups, combined with kidnappings, assassinations, and other subversions to obtain their technical expertise and move their attention away from the Empty Synod. If the Mechanicus found out that the Empty Synod uses silica animi, it would provoke a war between the two groups, a war the Empty Synod does not yet feel it is ready to wage. Instead, the Empty Synod uses the backdoor trade to win the Mechanicus' good will for their various fronts.
The Inquisition: The Inquisition is aware of the "Conventus Vanitas", but the vast majority of its membership who are aware of them have been led to believe they are relatively mundane criminals and political reformers more suitably dealt with by planetary officials. The Empty Synod seeks to subvert a handful of the most radical Inquisitors to use their power on its behalf. A recent setback has been two Monodominant Inquisitors who have discovered the Empty Synod's existence and have formed an "Ordo Vanitas" to investigate further. Their working understanding is that it is some form of Chaos cult.
Infractionists: Infractionists are often great recruits for the Empty Synod, though most don't go beyond being "Pseudophoroi", deniable assets. A handful of famous and highly skilled criminals are recruited to become Taxiarchs, where their skills at evading Imperial power are put to good use. Criminal gangs are an extremely common kind of front group for the Empty Synod to establish as a first approach to a new system.
Rogue Traders: The Empty Synod is known to Rogue Traders as some sort of xeno confederation active in the Halo Stars, though the two groups primarily deal with one another through third-party intermediaries.
An Empty Synod Patron: Raskol Might, Taxiarch
Raskol Might is a former arch-criminal who is currently living under the false identity of "Samson Phunic", guildmaster of Solomar Holdings for the Bhadra system. He is the Empty Synod's Taxiarch for Bhadra, responsible for the subversion and eventual overthrow of Imperial governance of the system.
Might is legendary amongst infractionists for a series of high-profile frauds and heists two centuries ago that stripped hundreds of millions of gelt from the Globe subsector's nobility and clergy and diverted them to hundreds of thousands of underhivers. "The Great Nuust Giveaway", "the Qurmizi Ship Swap", and "the Hubris of Namar Pratik" are still studied by auditors and enforcers looking to piece together how he pulled them off. Many of his targets were later revealed to have gained their wealth through means so foul that the Inquisition was called in to punish them, the investigations sparked by Might's thefts.
Since that burst of activity, Might has periodically reappeared to groups of infractionists, offering them leads, plans, and resources to conduct some amazing heist or con themselves, though he quickly vanishes after the initial support, leaving the successful execution up to the groups he has aided. Many fail for their own reasons, but the few who succeed contribute to the legend of Raskol Might.
In his "Samson Phunic" identity, Might spends his days using his analytical skills to advance Solomar Holdings' interests in the Bhadra system. He has been in place for nearly a decade, slowly recruiting agents, calling in favours, and summoning old allies and proteges to gather around him, all while strategising about how to overthrow the system.
Recently, he received a communique: The time has come for Bhadra to fall.
Faction: Infractionist (The Empty Synod)
Duty: Guildmaster (Might lives as the senior executive "Samson Phunic" at Solomar Holdings)
Motivation: Conflict (Might's goal is to undermine Imperial rule on Kangyur)
Duty Boon: Registered Trader (Might can secure trade records, passage on Solomar Holdings Chartist vessels, and can acquire anything for his agents from the Armoury section of the rulebook at a 30% discount)
Forger: Might can, with a bit of time, create almost any document or authorisation needed.
Tentative Alliance: Might is constantly favour trading via Solomar Holdings with various mid-level members of the Adepta; PCs can choose a faction before each mission and gain +1 patron influence with them.
Demands Discretion: Might's name, and therefore patron influence, should only be invoked in front of people who are opposed to the Imperium's rule; Solomar Holdings's involvement should be kept far away from anti-Imperial activities.
Impostor: "Samson Phunic" is a fake identity, Might is wanted in a score of star-systems under his own name. Avoiding connection between the two identities is highly important.
Overextended: Might spends most of his days managing a business empire stretching across multiple planets and with interests in a dozen systems. He gives his teams a great deal of freedom and discretion, but also can't spend much time supporting them in the field.
(Raskol Might is the PCs' patron)