The Horus Heresy is a dark, far-future military space opera[2] concerning a galactic civil war within the nascent Imperium of Man, and which constitutes a cornerstone event of the dystopian science fantasy Warhammer 40,000 universe.
Organised in numerous expeditions, the Crusade fields huge fleets and vast armies; at its forefront, led by the Primarchs, are Legions of Space Marines – genetically enhanced supersoldiers numbering in the millions.
[12] Humankind's continuing biological and psycho-spiritual evolution includes the gradual development of widespread Warp-related psychic abilities that will make the species far more susceptible to Chaotic influence; united under the Imperium of Man, the Emperor seeks to protect all of mankind by using faith in the Imperial Truth as a shield.
The novel details the first open move of the Heresy, the "Betrayal of Istvaan III", wherein factions of four Astartes Legions who were deemed unconvertible by their traitor brethren are ambushed during a planetary invasion of the fictional Isstvan star system.
Garro and the others on board the vessel face suspicion and incredulity from Imperial authorities; apart from the inconceivable news of Horus' betrayal, the situation is complicated by the fact that many of the travellers on the Eisenstein now openly proclaim their belief in the Emperor's divinity, itself a heresy.
Early in the Heresy, the Traitor Word Bearers Legion is tasked with organising and leading the invasion; they plan to use an immense, secretly commissioned warship, the Furious Abyss, to spearhead the surprise attack.
Kelbor-Hal, Fabricator General of Mars and the technocracy's supreme leader, declares for Horus, and together they carry out a coup d'état to eliminate Techpriest and Magos adherents of the Cult who are loyal to Terra and the Emperor.
This anthology contains the following stories: Blood Games by Dan Abnett, Wolf at the Door by Mike Lee, Scions of the Storm by Anthony Reynolds, The Voice by James Swallow, Call of the Lion by Gav Thorpe, The Last Church by Graham McNeill and After Desh'ea by Matthew Farrer.
There have been several previous unsuccessful attempts against Horus' life, and this gives a high-ranking officer of the Traitor Word Bearers Legion the idea to field a nemesis weapon of his own: a highly specialised assassin, who is to be used in an audacious scheme to kill the Emperor.
The despairing Lorgar is subsequently swayed by two of his most trusted lieutenants, who are in secret allegiance with Chaos; eventually both Primarch and Legion covertly embrace (and promote) the Primordial Truth, many years before Horus' corruption.
[27][28] This anthology contains the following stories: Rules of Engagement by Graham McNeill, Liar's Due by James Swallow, Forgotten Sons by Nick Kyme, The Last Remembrancer by John French, Rebirth by Chris Wraight, The Face of Treachery by Gav Thorpe, Little Horus by Dan Abnett, The Iron Within by Rob Sanders, Savage Weapons by Aaron Dembski-Bowden.
The novel features the reappearance of The Cabal (Book 7), and of other well-known characters; it also adds information about the developing strategies and subterfuge applied by the opposing sides, including reasons for Horus' timetable and for the Emperor's actions during the initial stages of the Heresy.
Unaware of the developing rebellion and the Word Bearers' true role and allegiance, Primarch Roboute Guilliman and his Ultramarines are unprepared for the underhand invasion: it is total, bloody war, with ritualistic undertones, scorched earth tactics, decisive use of technology, and the considerable involvement of Chaos; the inconceivable treachery and its implications forever change the Loyalists' view of reality.
[32] The novellas further develop these characters, who make multiple appearances in the series: following the Dropsite Massacre (Book 5), Fulgrim, perversely empowered by his own corruption, reveals his true nature and future plans to top officers of his compromised Legion; during a Great Crusade campaign against the enigmatic Eldar, Ferrus Manus, already beset by unsettling dreams, is subjected by alien sorcerers to stark, portentous visions and warnings about his future and role in the soon to be revealed Heresy; with Horus' rebellion in full swing after the events of Isstvan V, a suspicious and isolated Lion El'Jonson accepts the newly revealed realities of the Warp and decides on an independent course of action for the Dark Angels in the unfolding conflict; around the same time, and plotting a typically indecipherable course in the expanding war, the twinned Primarch of the Alpha Legion is involved in a unique counterintelligence operation that extends the Legion's customary deceptions inwards.
Sanguinius and his Legion, now fully aware of the great betrayal and the reality of Chaos, race to the defense of Terra and the Emperor while buffeted by unprecedented navigational difficulties; it is hinted that these are related to the action in the Ultramar system of Calth (Books 19 and 24).
In tenuous and fragile cooperation, the two very different Traitor Legions lay waste to worlds across Ultramar; it is a "Shadow Crusade" meticulously planned by Primarch Lorgar of the Word Bearers, who deploys Abyss-class spaceships.
The book adds more background concerning the battle at Istvaan V, at the same time showing the drama of a squad of his surviving sons and the shattered legions while they fight to retrieve an unknown artifact that will change the course of history in the coming days of the rebellion.
Strange events start to happen after the arrival of members of the Cabal organization; a Word Bearer Legionnaire seeking redemption for his Legion and the Night Lords' Primarch begin their search for an unknown "object" that fell from orbit straight to the hands of Guilliman.
With the destruction of the device responsible for maintaining the warp storms (as detailed in the short story, The Serpent Beneath, found in Book 20), the White Scars begin to receive a flood of conflicting information.
Caught betweens this opposition and the internal psychological damages his legion is suffering from attrition warfare, Jagathai Khan and his allies turn their efforts to uncovering another path to Terra, one that unearths secrets of the divided Navis Nobilite and the Emperor Himself.
The Emperor of Mankind, alongside the ‘Ten Thousand’ Custodian Guard, the Sisters of Silence and the Mechanicum forces of Fabricator General Kane, fight to control the nexus points of the ancient eldar webway that lie closest to Terra, now infested by daemonic entities after Magnus the Red's intrusion.
But in order to be ready to confront his much-changed brother, Leman needs to journey into the depths of his homeworld, and come to terms with the burdens of his duty as the Emperors' Executioner, his Spear that never wants to leave his side, and the realities of his nature as a Primarch.
The third part of the story is largely unrelated to the Death Guard, and follows Garviel Loken and Nathaniel Garro, alongside several other characters, as they form the Grey Knights Chapter of Space Marines upon the eve of the Siege of Terra.
Amidst the fighting, former remembrancer Mersadie Oliton desperately searches for a way back to Terra, a disgraced Sigismund seeks atonement through battle, Abaddon cleaves out a path laid out for him by both his primarch and darker powers, and Ahriman prepares a ritual that might determine the success of the Traitors.
But more than the Walls and the Loyalist Primarchs are needed to be tackled to gain entry, and Abaddon has to contend with the divisions to the Traitor forces while Horus continues his psychic assault upon the Emperor even as his body is being slowly consumed by Chaos.
Rogal Dorn on the other hand must begin to make hard choices to keep the palace secure until Roboute arrives, and in opposition to his growing desperation creates an order of scholars to document (and conceal if necessary) the history of the civil war.
With the Traitor Titans and the Loyalist Legio Ignatum set on a collision course at Mercury Wall and a sealed order from the Emperor given to Dorn, outside the Palace Paladin Corswain of the Dark Angels must make a desperate ploy that might change the course of the Siege, and the Perpetual Ollanius Persson must journey through the tortured insanity of the warp and his own memories if he and his allies are to reach Terra and his unknown future... 60.
Warhawk As the Palace defenses continue to weaken both physically and metaphysically, Jaghatai Khan makes a dangerous gambit to retake the Lion's Gate spaceport from a mutated Mortarion and the now-fully corrupted Death Guard.
With the Khan on the edge of death, Dorn beleaguered at the Bhab Bastion, and Guilliman (seemingly) not going to make it in time, it falls to Sanguinius – fated-to-die and the Angel of the Ninth Legion – to rally the defenders and refugees for one more stand at the Delphic Battlement, the very walls of the Sanctum Imperialis, and paint the golden Eternity Gate blood red if he must if it means the Traitors shall not pass.
At the same time, Ollanius Persson and his "Argonauts" reach the Palace, hoping to warn the Emperor that Horus' power has grown to the point where he will sacrifice humanity to become a new God of Chaos, "the Dark King".