Execution Force - 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.