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An Execution Force comprised of an Eversor Assassin, Culexus Assassin, Callidus Assassin and a Vindicare Assassin

An Execution Force is a highly specialised ad hoc formation comprised of the most deadly Imperial Assassins from every temple, dispatched by their temple masters under the direct orders of the High Lords of Terra to take out the deadliest of targets.

The first known use of an Execution Force was during the opening days of the Horus Heresy, following the Warmaster Horus' treachery during the Istvaan III Atrocity, unleashed on the direct order of Malcador the Sigillite, Regent of Terra.

This Execution Force initiated a bold attempt to assassinate the Arch-traitor Horus upon the world of Dagonet. Ultimately, their assassination attempt failed and all but one of the Assassins were slain by the Traitors.

Execution Forces are still used for rare but critical missions in the 41st Millennium.


The secretive organisation known as the Officio Assassinorum is comprised of various "temples" that train Human Assassins to further the goals and protect the security of the Imperium of Man.

Although the Inquisition strikes fear in the hearts of all Imperial citizens, loyal and corrupt alike, the deadly disciples of the Officio Assassinorum strike fear in the hearts of even the most savvy, battle-hardened of Imperial warriors.

Silent, deadly and ruthlessly efficient, an Assassin can strike like a scalpel at the heart of the problem, quickly and cleanly removing those who would dare oppose the Emperor. Impassive and impersonal, an assassination sends a clear message to Heretics and apostates -- no one is beyond the Emperor's justice.

However, there are certain dire circumstances that necessitates the use of more than a single Assassin in order to accomplish the objective.

During such times, the High Lords of Terra have often granted special dispensation to dispatch an Execution Force comprised of a number of hand-picked Assassins, from either the same temple or a mixed force from more than one temple, to work in concert, in order to accomplish their singular goal of assassinating the most deadly of targets who are classified as "threat level omega".

A perfect example was when the Imperium deployed an Execution Force sometime in the 41st Millennium to seek out and slay the so-called Chosen of Abaddon -- four powerful Chaos Lords that served under the patronage of Abaddon the Despoiler, the Warmaster of Chaos and master of the Black Legion of Chaos Space Marines.

Such highly specialised units are only deployed in the most desperate of times, for to deploy even a single operative is a full committal of the most valuable of Imperial resources.

To deploy an entire Execution Force in such a way is considered the most desperate of gambles as the loss of such a team would have serious repercussions for the Officio Assassinorum, who might take many solar decades to replenish their ranks with such potent operatives.

First Execution Force

Iota, of the Culexus Clade, searches for her quarry upon the world of Dagonet during the Horus Heresy.

After learning of Horus' perfidy on Istvaan III, the sires and siresses of the various secret Imperial Assassin Clades, as the temples were originally known during the time of the Great Crusade, were tasked by Malcador the Sigillite, the secret Grand Master of Assassins, with the daunting task of slaying the Arch-traitor Horus.

If they could accomplish this monumental undertaking, they could effectively crush the nascent rebellion against the Emperor before it could inflict further damage upon His Imperium.

But every assassination attempt against the Renegade Warmaster had failed. Though the operatives sent by the clades were their finest students and equal to the task, every attempt had resulted in failure.

The Assassins had thrown their most gifted students into a meat-grinder, sending them in blind and half-prepared.

Every strike against Horus was broken, and he had shrugged off each attempt without notice. Every time the Clade masters met, they were forced to grimly listen to a catalogue of each other's failures.

After the last failed attempt by Clade Venenum, a new strategy was decided upon. With the advice of a special guest in the form of Constantin Valdor, the Captain-General of the Legio Custodes who served as the personal protectors of the Emperor, the masters of the clades realised that their mission plans were not flawed, they were simply not enough.

No single Assassin, no matter how well-trained, no matter which clade they hailed from, could ever hope to terminate the Arch-traitor alone. But a collective of killers, a strike team consisting of an elite unit of Assassins from every clade hand-picked for the task, might be enough to succeed.

There had never been a precedent for such an initiative, for the Emperor would have never sanctioned assassination as an official Imperial policy. The deployment of an Assassin was a delicate matter and never one taken lightly.

In the past, the clades had fielded two or three of their operatives on a single mission when the circumstances were most extreme, but these Assassins were always drawn from the same clade, and even this occurred only after much deliberation.

Yet in this crucial and extreme instance, Malcador, serving as director primus of the clades, decided that more drastic measures were needed to accomplish the Assassins' singular goal. He authorised the creation of the first Imperial Execution Force.

Horus did not adhere to the rules of war, nor did he baulk at the use of a tactic because it offended delicate sensibilities. At Istvaan III he had bombed his sworn brethren, his own warriors even, into obliteration. Nothing, no matter how vile, was beyond him.

It was decided by the Assassins that if they were to kill this foe, they could not limit themselves to the moral abstracts that had guided the clades in the past. They had to dare to exceed them.

And so a select strike team of Assassins was formed. A so-called "Execution Force," the first of its kind. Six Assassins, one from each clade, were gathered together and given the select task of killing Horus by any means necessary.

In the meantime, the Dark Apostle Erebus had decided on a bold course of action of his own. He firmly believed that as long as the Traitor Legions followed Horus, all would be as it should and as the Dark Gods had promised.

Victory would come soon enough, perhaps even sooner than any of them might expect, for after the latest assassination attempt on the Warmaster, Erebus had come to realise a truism of warfare: if a tactic could be used against Horus, then it could also be used by the Traitors against the Emperor.

"Black Pariah"

Within Imperial history, only one "Black Pariah" has ever existed. He was a former Imperial Assassin by the code-name of "Spear." Born as a Human Untouchable, he was captured by the Silent Sisterhood and brought to Terra, where the Clade Culexus experimented upon and augmented him in an attempt to create a more powerful and deadly form of Culexus Assassin.

It is not known whether these augmentations or his unnatural abilities made him a "Black Pariah." Spear was eventually deemed too unstable and dangerous by his clade's masters to be left alive. He was placed in the care of the Sisters of Silence and was sent aboard one of their lone vessels, bound for the heart of a nearby sun.

Unfortunately, this vessel was intercepted by a Traitor vessel carrying the Dark Apostle Erebus of the Word Bearers Legion. Boarding the sisters' vessel, the Word Bearers killed all aboard, with the exception of Spear.

Sensing the usefulness of such a unique specimen, Erebus found a new purpose for his captive. He forced Spear to undergo a painful and vile Chaos ritual, in which a minor Daemon from the Immaterium was bonded with the former Imperial Assassin.

This bonding created a highly dangerous apex predator -- a "counter-psyker" -- capable of redirecting a psyker's attack directly back upon them. In order to utilise this ability, the "Black Pariah" first had to obtain a sample of his target's blood. This was a necessary component that helped him synchronise with his target's psychic abilities in order to reflect their attacks.

Two standard years later, following the events of the Drop Site Massacre on Istvaan V, Erebus tasked his deadly minion to assassinate the Emperor.

Spear spent an inordinate amount of time in order to painstakingly reach his ultimate goal -- a document that possessed a minute drop of the Emperor of Mankind's precious blood.

Spear eventually obtained this document upon the world of Dagonet, which would bring him into direct conflict with the Imperial Execution Force.


As the Horus Heresy progressed and word filtered throughout the galaxy of Horus' galactic uprising, numerous worlds began to erupt into anarchy as the populations began to split over whether they should remain loyal to the Emperor or join the Warmaster.

Dagonet was one such world, where Horus Lupercal was second only to the Emperor in being celebrated by the people of the planet; statues in Horus' honour were raised everywhere, and the Dragoneti spoke of him as "the Liberator."

As the historic record went, in the early years of the Great Crusade, Dagonet had languished under the heel of a corrupt and venal priest-king who ruled the planet through fear and superstition.

Horus, at the head of his Luna Wolves Legion, had come to Dagonet and freed the world -- accomplishing the deed with only one round of ammunition expended, the single shot he fired that dispatched the tyrant of Dagonet. The victory was one of the Warmaster's most celebrated triumphs, and it ensured he would be revered forever as Dagonet's saviour.

The Dagoneti clans had started the uprising against the Imperium when the Heresy began. The Imperial planetary governor issued a formal statement of support for the cause of Horus. The world's nobles had declared in favour of Horus and rejected the rule of Terra. The common people were the ones fighting back in the name of the Emperor.

There was blood in the streets of the Dagoneti capital city as soldiers fought soldiers and militia fought clan guards. Those who could flee the star system filled every starship they could get their hands on.

It was small wonder that the aristocratic clans who now ruled the planet would give their banners to Horus instead of a distant Emperor who had never set foot on their world.

The Execution Force soon learned the future whereabouts of where Horus would be. Agents of the Imperium operating covertly in the Taebian Sector report a strong likelihood that Horus was planning to bring his flagship, the Vengeful Spirit, to the planet Dagonet in order to show his flag.

The clades believed that the Warmaster's forces would use Dagonet as a foothold from which to secure the allegiance of every planet in the Taebian Stars Sector. Dagonet was a keystone world in the politico-economic structure of the Taebian Sector, and if it fell fully under the shadow of Horus, then it would mark the beginning of a domino effect, as planet after planet along the same trade axis followed suit.

Every Loyalist foothold in this sector of space would be in jeopardy. One Imperial vessel would be able to slip through the Warp to Dagonet, far easier than an entire reprisal fleet. Six Assassins, the best of their clades, could bring death.

The Execution Force would embed on Dagonet and set up multiple lines of attack. When Horus arrived there, they would terminate his command with extreme prejudice. Horus' assassination at this juncture would throw the Traitor forces into disarray and break the rebellion before it could advance on to the Segmentum Solar.

The Execution Force successfully circumvented all detection and was able to secretly arrive upon Dagonet. The Execution Force gathered intelligence to determine what exactly had occurred on Dagonet. In the first moments of the insurrection, desperate signals had been sent to the Space Marine Legions and their Legion fleets; but these had gone unanswered.

Both the starships of the admiralty and the Legions had battles of their own to fight, far from the Taebian Stars. They would not intervene. For all the fire and destruction the collapse of Dagonet and its sister worlds might cause, there were larger conflicts being addressed; no crusade of heroes was coming to ride to the rescue.

The civil war on Dagonet was a rout, and it was those who stood in the Emperor's name who were dying. Across the planet, the forces that carried Horus' banner were only solar days away from breaking the back of any resistance. Dagonet was thus already lost to the Imperium.

The turncoat nobility on Dagonet did not need to see Horus to adhere to his banner. His influence hung over Dagonet like an eclipse blotting out the sun. They were fighting in his name in fear of him, and that was enough. And when the Traitors finally won, Horus' work would be done for him.

This same thing was happening all across the galaxy, on every world too far from the Emperor and the rule of Terra. When Dagonet fell, Horus would turn his face from this place and move on, his advance one step closer to the gates of the Imperial Palace.

While gathering intelligence and deciding upon the best course of action, two of the Execution Force's number decided to set about on a different course of action. The Venenum Assassin Jenniker Soalm had become distracted by her mission with the plight of the local Loyalist Dagoneti who continued to wage their desperate war against the pro-Horus planet's nobility.

The Dagoneti introduced her to the forbidden writings of the Lectitio Divinitatus which postulated the worship of the Emperor of Mankind as a divine being, the one, true God of Humanity. Some became a willing convert of this nascent religious movement and vowed to help the Dagoneti with their plight.

Her interest in helping the people of Dagonet and her new spirituality created friction with the rest of the Execution Force, and so she took her leave, and the mission to assassinate Horus continued on without her. The Culexus Assassin Iota, who showed great interest in Soalm's quest, followed her.

The pair of Assassins soon came into conflict with the "Black Pariah" known as Spear. Realising the dire threat of such a creature, the two Assassins attacked the Traitor Assassin. In the ensuing battle Soalm was mortally wounded. Iota utilised her Animus Speculum, unleashing her innate anti-psyker abilities upon Spear, seriously wounding him in the process.

Though Iota finally gained the upper hand, her efforts were for naught, as Spear was able to sample a drop of her spilt blood.

This enabled the Traitor Assassin to engage his genetic lock, using his own innate Pariah abilities to reflect Iota's attack back onto her, boiling the Assassin in the crucible of her own powers.

The dying Soalm was found by her brother Eristede Kell, a Vindicare Assassin and the Execution Force's team leader. Soalm made Kell promise to kill the Traitor Assassin, not out of vengeance, but for the sake of the God-Emperor.

The Execution Force managed to salve Iota's memory coil from her Animus Speculum and review her confrontation with the creature known as Spear.

Realising the dire threat that this Counter-Assassin represented, the Assassins' mission became twofold; assassinate Horus and kill the creature that had murdered their comrade.

Moment of Truth

The Sons of Horus Legion finally arrived in-system at Dagonet. The Vengeful Spirit settled in orbit above Dagonet. The vessel had brought a military force of such deadly intent and utter lethality that the planet and its people had never known the like in all their recorded history. And it was only the first.

Other Traitor warships were following close behind. This was the visitation granted to Dagonet by the Sons of Horus, the tip of a sword blade forged from shock and awe. Far below, on the planet's surface, across the white marble of Liberation Plaza, a respectful hush fell over the throng of people who had gathered.

A pregnant hush fell over the Dagoneti, as they looked to the sky and awaited the arrival of their redeemer, the owner of their new allegiance. Their war-god, the Warmaster Horus.

At this time, the Execution Force was in place. The Vindicare Assassin Kell waited in the perfect assassin's perch, ready for the Warmaster's arrival. The Callidus passed a measuring gaze over the nervous lines of Dagoneti Planetary Defence Force soldiers and the robed nobles standing back on the gleaming, sunlit steps of the great hall.

Governor Nicran was there among them, waiting with every other Dagoneti for the storm that was about to break. Suddenly, there was a blast of fanfare from the trumpets of a military band, and Governor Nicran stepped forward.

When he spoke, a Micro-bead at his throat amplified his voice. "Glory to the Liberator!" he cried. "Glory to the Warmaster! Glory to Horus!" The assembled crowd raised their voices in a thundering echo.

The Sons of Horus teleported onto the planet's surface. The tallest of the transhuman warriors, his battle gear decked with more finery than the others, stepped forward. He was covered with honour-chains and combat laurels, and about his shoulders he wore a metal dolman made from ores mined in the depths of Cthonia; the Mantle of the Warmaster, forged by Horus' captains as a symbol of his might and unbreakable will.

He drew a gold-chased Bolt Pistol, raising it up high above his head; and then he fired a single shot into the air, the round crashing like thunder. The same sound that rang about Dagonet on the day they were liberated. Before the empty shell casing could strike the marble at his feet, the crowd were shouting their fealty. "Glory to Horus!"

The towering warrior holstered his gun and unsealed his helmet, drawing it up so the world might see his face. This was the moment of truth. The Vindicare Assassin placed his crosshairs on the centre of the scowling grille of the Warmaster's helmet. There was no hesitation, no margin for error.

The Assassin fired his Exitus Rifle. The shot struck the target in the throat, reducing the flesh to atoms, superheating the fluids into steam, boiling skin and vapourising bone.

The only sound was the fall of the headless corpse as it crashed to the ground, blood jetting across the white marble and the Warmaster's shining mantle. Horus was dead.

But the Assassins of the Execution Force had been duped. Horus had sent a surrogate, a sacrificial proxy. The Vindicare had killed Luc Sedirae, the captain of the Sons of Horus' 13th Company.

Though the warrior Kell shot wore the mantle of the Warmaster, the unique robe belonging to the primarch himself, it had all been a ruse. In their anger, the Sons of Horus turned upon the populace of Dagonet and began to slaughter them in earnest.

Amidst the chaos and anarchy of the massacre of the entire populace of Dagonet, Kell finally tracked Spear down and with the assistance and sacrifice of his fellow Assassins, managed to finally draw out and kill the "Black Pariah."

Kell found himself the lone survivor of the first Imperial Execution Force. The Vindicare Assassin departed Dagonet and decided to make one last attempt on the Warmaster's life.

He made a suicidal attack on Horus' flagship. Kell set his own ship on a direct course for the Vengeful Spirit's command bridge, where he seemed to meet his own fate when he ejected himself into space once he reached his intended target, in an ultimately vain attempt to land a desperate shot at Horus while he stood looking out of the battleship bridge's armoured observation deck into space.

The Execution Force's assassination attempt had failed.

In the aftermath of the events on Dagonet, Horus confronted Erebus. He chastised the Dark Apostle for his audacious plan to assassinate the Emperor, declaring that when the opportune moment finally dawned, it would be him -- and him alone -- who killed his father, the Master of Mankind.

Notable Execution Force Members

  • Koyne - Koyne was a Callidus Assassin during the Great Crusade and opening days of the Horus Heresy. Koyne was a shade of Clade Callidus ranked as an Epsilon-dan, the senior-most rank of the order. Having been a shape-changer for most of his/her life, Koyne often stayed in the form necessary for the completion of the mission and eventually had forgotten his/her original gender.
  • Iota - Iota was a female member of the Culexus Clade during the Great Crusade and Horus Heresy era. Iota was designated as a protiphage, for she was not fully Human in the strictest sense; she was a clone, or as they were known in the Imperium, a replicae. Created by the Emperor's biologians, Iota was conceived from cells that had been combined in a test tube in a laboratory. As a Culexus Clade operative she was a being without a soul, closer to a xenos than her own kind.
  • "The Garantine" - The Clade Eversor Assassin known only as "The Garantine" was a nihilator of his clade who was ranked as an Epsilon-dan, the senior-most rank of his order, and was active during the Great Crusade and the opening days of the Horus Heresy. His original name forgotten, the operative codenamed "Garantine" was so-named because it was said he hailed from the Garant Span, an Oort Cloud collective on the near side of the Perseus Null. A natural psychotic, he had killed everyone on his home asteroid, and all this as a child barely able to read. It was no wonder the Clade Eversor had been delighted to take ownership of him.
  • Fon Tariel - Fon Tariel was a Vanus Assassin during the Great Crusade and the opening days of the Horus Heresy. He was an infocyte of the Clade Vanus ranked at Epsilon-dan, the senior-most rank of his order.
  • Jenniker Soalm - Jenniker Soalm, born Jenniker Kell, was a Venenum Assassin during the Great Crusade and opening days of the Horus Heresy. She was a secluse of the Clade Venenum ranked at Epsilon-dan, the senior-most rank of her order.
  • Eristede Kell - Brother to Clade Venenum Assassin Jenniker Soalm, Eristede Kell was a Vindicare Assassin during the Great Crusade and opening days of the Horus Heresy. He was an assassin-at-marque of Clade Vindicare who was ranked an Epsilon-dan, the senior-most rank within his order.


  • Codex: Chaos Space Marines (3rd Edition, 2nd Codex), pg. 10
  • Nemesis (Novel) by James Swallow
  • Assassinorum: Execution Force (Novel) by Joe Parrino