History Literature / HorusHeresy

* KickTheSonOfABitch:
** You can't help but cheer a little when [[spoiler: Fulgrim kills Eidolon in ''The Reflection Crack'd'']].
** It's fair to say that nobody particularly minded [[spoiler:Horus peeling off Erebus's face at the end of ''Fear to Tread'']]. Some even cheered.
** Vulkan mocks Konrad Curze to his face before beating the shit out of him with his hammer and teleporting out.

* BrotherhoodOfFunnyHats: This is what the members of the warrior lodges claim their little clubs are, despite the protestations of more resistant Astartes who see them as an unnecessary and potentially subversive adulteration of the legions' social hierarchy. They're right to be concerned, as it turns out the lodges were a TrojanHorse designed to do precisely what the naysayers feared would happen: turn a seemingly-innocent gathering of friends into a tight-knit in-group who could then be more easily turned against anyone who was deemed to be an "outsider", regardless of rank or friendship, which the lodges' secret code phrases and rituals only helped to reinforce. Some members eventually see what's happening and get out in time, but many more do not, which eases their transition into treason.

* [[WhamEpisode Wham Chapter]]: When The Emperor makes an appearance, it usually has huge repercussions for the greater narrative.

** ''Vengeful Spirit'', which is a Wham Episode for the series [[spoiler: exploring [[DealWithTheDevil why]] the Emperor is so powerful and [[SuperEmpowering empow]][[TrainingFromHell ering]] a now completely evil Horus to a similar extent.]]

** In "The End and the Death: Volume II", it's revealed that the fifth Chaos God, the Dark King is indeed ascendant, and it's in fact [[spoiler: the Emperor. He's been gorging himself on Warp energy to give him the strength to vanquish Horus, but rejects it after being convinced by Ollanius, Garviel, and Leetu, and removes his compassion, in form of a "child like a star". ]] Also, Sanguinius dies.
* WhamLine: In ''The Outcast Dead'':
-->'''Kai Zulane''': [[spoiler: But you're going to die.]]\\

-->''Written in flowing script were the words "[[spoiler:The Unbound Flame]]"''.

-->''"Know me by the name I always had," he said. "Call me [[spoiler: Ianius]]."''

-->[[spoiler: ''It is not Horus Lupercal.'']]

* DropTheHammer: Some Space Marines forgo the usual power sword for hammers and maces of various description. Hammers are Ferrus' and Vulkan's preferred weapon, too. After Ferrus dies, Horus gives his hammer to Perturabo.

* {{Doorstopper}}: The Siege of Terra books are all hefty enough to qualify, especially in hardback, but the crown goes to ''The End and the Death'', which clocks in at a whopping 1,664 pages split across three volumes.

** In ''The End and the Death'', [[spoiler:Terra itself has become this, as Chaos has begun to submerge the entire world into the Warp, and space and time are being corrupted as a result. It begins with roads seeming to stretch on forever, people being separated in a crowd and ending up miles apart from one another, and traitor forces appearing behind loyalist lines; but it rapidly gets worse and worse until the Imperial Palace starts to occupy the same space as the ''Vengeful Spirit'', creating a corrupted and incomprehensible labyrinth. To illustrate how bad it's getting, the Adeptus Custodes, who are supposed to have absolutely perfect knowledge of the Palace's layout, find themselves getting hopelessly lost within moments of leaving the (relative) safety of the Throne Room.]]

** Samus is watching. Samus is all around you. I am Samus.

* AuthorityEqualsAsskicking: More or less a requirement for being the First Captain of a Space Marine Legion. Ezekyle Abaddon of the Luna Wolves/Sons of Horus, Sigismund of the Imperial Fists, Raldoron of the Blood Angels, Sevatar of the Night Lords, Jubal Khan of the White Scars (though the Khans aren't given numbers, he's the most prominent after the Noyan-Khans) and Gabriel Santar of the Iron Hands are all considered the best warriors of their respective Legions. Even the more intellectually inclined Legions' First Captains, such as Ahzek Ahriman of the Thousand Sons and Ingo Pech of the Alpha Legion, are noted for being formidable warriors. [[SinisterMinister Kor Phaeron]], as First Captain of the Word Bearers, [[spoiler: defeated Roboute Guilliman in single combat, and could have killed him had he not decided to try his hand at corrupting him.]] He is arguably the single most formidable combatant in the Legions that is not a Primarch.

* BelowDecksEpisode: The entirety of ''Legion'' plays out from the POV of human characters swept up in the Alpha Legion's web of deceit.

* BodyguardBetrayal: A cruel example in ''The End and the Death''. When the Emperor teleports into the Vengeful Spirits, his [[spoiler:own Custodes bodyguards]] attack him, being overcome by Chaos. This even manages to anger the Emperor because [[spoiler:the Custodes]] were His companions, and not just his soldiers.

** During the Siege of Terra, the loyalists' hope is to hold out until Roboute Guilliman and Lion El'Jonson arrive with their Legion to crush the traitors from behind. [[spoiler:Alas, the interior wall is breached before the loyalists can arrive, which will lead to the Emperor teleporting aboard the ''Vengeful Spirit''.]]

* ComputerVirus: In ''Mechanicum'', the Dark Mechanicum spreads a scrapcode (a warp-infested computer virus) across Mars, hacking and corrupting all the pieces of technology it touches. Because of their great use of cybernetics and noospheric connections, most of the Mechanicum on Mars was exposed and corrupted to Kelbor-Hal's side. The same tactic appears in ''Know No Fear'' and ''The First Wall'', with Chaos-tainted scrapcode used to cripple loyalist noospherics and communications.
* ConflictingLoyalty: Many of the Astartes in the Traitor Legions suffer from this: who first, their Primarch or the Imperium?

* DeadMansSwitch: In ''Old Earth'', the Emperor finally turns the Golden Throne into one after Vulkan inserts the Talisman of Seven Hammers (that the Emperor himself forged in Nocturne by commanding Vulkan's body) into its mechanism. If the Golden Throne fails or He dies, the Throne will engulf Terra in a roaring inferno, depriving Horus of the planet.

* DeathFromAbove: Long a favored trope of ''40K''

** During the Siege of Terra, the traitor fleet spends a great deal of time bombarding the absolute hell out of the planet.

* DividedWeFall: The Imperium of Man is fighting itself. In this corner, The Emperor and loyalist Primarchs and in the other corner, Horus and the traitor Primarchs. The main theme of ''Umremembered Empire'' is that Imperium Secundus and by extension mankind will only survive the Horus Heresy by trusting each other. Ultramar is threatened on several occasions by mistrust between its leaders, but they eventually come around and work together.

* DramaticSpineInjury: The enmity between the Space Wolves and Thousand Sons Astartes legions explodes into outright violence when the Space Wolves are dispatched to bring down the Thousand Sons after their Primarch Magnus the Red's disastrously failed attempt to warn the Emperor of Horus' treachery. While the two legions engage each other, a massive fight ensues between Magnus and Leman Russ, Primarch of the Space Wolves; they inflict serious injuries on each other, but Russ finally overpowers Magnus and breaks his back over his knee. However, Magnus uses Warp sorcery to remove himself and the surviving Thousand Sons from the battlefield before Russ can finally kill him.

** [[spoiler: Karkasy]]'s assassination in ''False Gods'' is covered up as this.

** [[spoiler: In ''The Buried Dagger'', Macer Varren blows himself up with a belt of grenades rather than allow himself to be possessed by the Lord of Flies.]]

* FirstNameBasis: The Astartes were ''friendly'' in Pre-Heresy times; some of them were, anyway.

** In ''The First Heretic'' First Captain Sevetar of the Night Lords become the first to utter the phrase "Death to the False Emperor!", the {{Battlecry}} that followers of Chaos have been using for ten thousand years.

* GhostPlanet: There are a great many in this Galaxy.

* GodEmperor: Constantly talked about, rarely featured directly. When he makes an appearance, it's often a eerie yet awe inspiring experience for those involved.

* GoMadFromTheIsolation: In ''The End and the Death'', Dorn teleports towards the Vengeful Spirit with the Emperor, the Blood Angels and a retinue of Imperial Fists but ends up alone in an endless SeaOfSand littered with the corpses of countless Imperial Fists as well as great walls. Dorn endures the isolation for what feels like centuries to him and slowly but surely goes mad, losing his memory, sense of identity, and his smallest weaknesses turning against him. It is revealed that he felt the pressure of having to organize the siege of Terra, and that sentiment is twisted into [[spoiler:a longing to spill blood for Khorne]].

%%* HaveYouToldAnyoneElse: In ''Legion''

* HeroKiller: [[spoiler: The Space Wolves are the Emperor's weapon of last resort: a Legion designed to kill another Legion.]]

* IAmSpartacus: All the Alpha Legion are Alpharius. It makes the scheming and unconventional warfare easier when the non-Legion don't know who's who. Exaggerated by the fact that apart from Alpharius himself, not even the Alpha Legionaries are aware which one of them is Alpharius at times.

* IncorruptiblePurePureness: Loken, Garro, Tarvitz, Keeler, Lord Commander Vespasian, and Qruze, all of whom remained loyal even when faced with the full power of Chaos. The first three are especially notable for being members of Legions that went wholesale traitor.

* InformedAbility: Played with in ''Horus Rising''. Loken is an admirer of the iterators, taking the opportunity to attend a speech given by primary iterator Kyril Sindermann, rigorously trained and the most famed member of his work, who gives a vapid sermon mostly consisting of a very thin argument, admitting near the start that [[MightMakesRight "I'm right and your wrong"]] isn't a very good debate point but ends the speech saying [[RightMakesMight exactly that]] and proclaiming the Imperial Truth. The speech itself is widely applauded by other iterators and Loken, one of the more aware Astartes in the series, doesn't question it in any serious way. The narration even admits that some of the audience members were planted to get applause going. It adds onto the theme of the pre-Heresy Imperium being an intellectually bankrupt authoritarian state, better in ways but not too drastically different to the theocratic dystopia it would become, and many of its followers and agents are just as indoctrinated.

* TheLastDJ: Several of the loyalist members of the Traitor Legions fit the trope, particularly Nathaniel Garro, Garviel Loken, Saul Tarvitz, and Barabas Dantioch. They are very good at what they do, highly respected by Astartes from other Legions, and represent the last vestiges of what their Legion used to be before it was taken over by their primarch and reshaped in his image. They frequently clash with other members of their legions over their loyalty to the Emperor and their insistence on holding onto the old ways. All this sees the marked for death when the Traitor Legions turn on the Imperium.

* LimitedSpecialCollectorsUltimateEdition: The Siege of Terra, Primarchs, and Character Series books have all received special editions, usually released a few months before the standard editions. To justify their price, they're limited to 2,500 copies apiece and come with autographs, fancy covers, gilt pages, and character art, among other things. As the series has gone on, many of the older books have received limited hardback reprints with extra art and new afterwords included.
* LongRunningBookSeries: Per the introduction. So much so that compared to the in-universe description of the Heresy's length (seven to nine years depending on the source), the series is pulling into the final stretch at fourteen years and counting.

** An observation and a bit of introspection by Kharn makes it clear that the modern Imperium of Man (in all it's VillainProtagonist glory/infamy) is ''entirely'' the Traitor Legions' fault, as it was the Heresy that moulded the Imperium from the somewhat egalitarian but relatively naive entity is was during the crusade into the oppressive and genocidal entity it is in ''40K'' that is nonetheless the greatest opponent Chaos faces.

* OutsideContextProblem: After the events of the Dropsite Massacre, we see a point of view of Corvus Corax, Primarch of the Raven Guard, where he muses over not being able to foresee Horus' betrayal. He decides that there is no way he could have foreseen it, because it should not have been possible.

** In ''Angel Exterminatus'', the Emperor's Children are scattered across the galaxy and the Legion devolves into individual warbands. The same happens to the Night Lords at the end of the Thramas Crusade, after Sevatar orders the fleets to scatter.

* PlaceBeyondTime: The Immaterium and [[spoiler:Horus's visions during his time in the Temple of the Serpent Lodge.]]

** The Custodes are this to the Emperor. They are the most powerful transhuman creations of the Emperor short of the Primarchs, and are usually tasked to guarantee his security.
** Many of the primarchs have honour guards whose official role is to bodyguard their leader. But since primarchs are already so powerful, these guards usually end up BodyguardingABadass and are more of an elite shock unit that support their primarchs instead. Some of the most notable examples are Mortarion's Deathshroud Terminators, who first appear in the series in ''Flight of the Eisenstein'' and cannot be further than 49 steps away from him; there's also Fulgrim's Phoenix Guard and Ferrus Manus's Morlocks, who have something of a malignant rivalry after Fulgrim's failed attempt to convert Ferrus to Horus' side before the Heresy begins in earnest, and the cadre of Phoenix Guard kills their counterparts in the Morlocks to escape. Rogal Dorn's Templars are officially tasked with guarding the Imperial Fists' Temple of Oaths on the ''Phalanx'', but also bodyguard Dorn in battle. Jaghatai Khan's Keshig are also another example, remarkable in that they are the only one wearing Terminator armour in a legion which prefers speed.
** Lorgar created one, the Gal Vorbak, fairly late, roughly 50 years before the start of the Heresy. They were formed from the surviving Astartes "expedition force" that returned from their excursion into the Eye of Terror, and came back... [[DemonicPossession changed]]. It's debatable if they're his bodyguard however, as in ''The First Heretic'' they fight separately from him, and have spent sixty years away until that point.

** Played with thoroughly during The End and The Death [[spoiler: regarding the Dark King. Part 1 gives every assumption that Horus will become the Dark King, which makes sense as he's the overall antagonist and is being empowered directly by all 4 Chaos Gods. However, due to time being locked into an eternal present during the end of the Siege, the Prophecy "slips" sideways - the Dark King will be incarnated either way. Unfortunately, it's the Emperor.]]

* TheQuest: ''Angel Exterminatus'' is basically the Emperor's Children and Iron Warriors travelling into the Eye of Terror to retrieve a powerful weapon named the ''Angel Exterminatus''. [[spoiler: It turns out to be a quest to raise Fulgrim to Daemon Princehood, with the Iron Warriors being used as pawns by the Emperor's Children.]]

** The Emperor is thought to be this by most characters in-universe, but when he actually acts or his plans are revealed it's clear to the reader that he's an aversion, being something of a JerkAss with the IdiotBall firmly glued to his hands and a tendency to intentionally prevent his legions from having [[PoorCommunicationKills effective intel or reconnaisance]] on their enemy.
* RebelliousRebel: Cutting this off was the reason for the Isstvan V attack -- and fomented it among the survivors. Also Garro, and the crew of the ''Eisenstein''.

* ResurrectiveImmortality: The Perpetuals, of which in story we meet Oll Persson, Alivia Sureka, John Grammaticus (who's a double winner, being a Perpetual psyker), and Vulkan. They can reform FromASingleCell and don't age, but every death makes them more insane.

* TookALevelInCynic: The story as a whole shows how the Imperium went from championing enlightenment and being relatively egalitarian into the theocratic empire that worships the Emperor as a god in the main ''40000'' timeline. It's best highlighted by the story of Euphrati Keeler, the founder of the Imperial Faith: at the beginning of the series, she turns to worshipping the Emperor after encountering an actual daemon, shattering her world view that gods and daemons do not exist. Her conversion leaves her with some odd mannerisms, but she's mostly a friendly person who provides support to several characters when they really need it. By the time the Siege of Terra rolls around, [[spoiler:Euphrati has started whipping up refugees into mobs that are suicidally charging toward the Chaos forces because there aren't enough resources for everyone in the refugee camps. Tellingly, this is the point where the Imperium's association with skulls really takes off, as several refugees take skulls with them as they March to their doom]].
* TheStarScream:

** Horus and Sanguinius spend quite some time trying to convince each other to switch sides. Additionally, when the former finds out that Erebus tried to have Sanguinius possessed, he rips his face off.

** Subverted with some of the loyalist Primarchs. Most of them are tempted to act as ruthlessly as possible in the war, notably when faced with daemons. Lion el'Jonson develops a nasty habit of using overwhelming force and Exterminatus on all tainted worlds; Guilliman is tempted to study and use the anathames against the forces of Chaos. However, both refuse to let these urges dominate them and notably come to the conclusion that extreme ruthlessness will drive the loyalist forces apart anyway.

* WeAREStrugglingTogether: In ''Slaves to Darkness'', the traitor legions are now clearly falling victim to grave infighting. Lorgar forces Fulgrim to join the conflict, while planning to overthrow Horus in the name of Chaos. Perturabo has to beat up Angron to get him to follow along too; meanwhile the Sons of Horus are at each others' throats regarding how to deal with a wounded and unconscious Horus. Magnus is technically part of the traitor forces, but is busy doing his own thing.

** In "The End and the Death: Volume II", it's revealed that the fifth Chaos God, the Dark King is indeed ascendant, and it's in fact [[spoiler: The Emperor. He does embrace power of the warp to vanquish Horus, but rejects it after being convinced by Ollanius, Garviel, and Leetu, and removes his compassion, in form of "child like a star". ]] Also, Sanguinius dies.

** In ''The End and the Death: Volume 1'', mention is repeatedly made of "the Dark King", [[spoiler: implied to be a fifth Chaos God potentially born from the end of the Heresy. Then four voices, implied to be the Chaos Gods, begin laughing and chanting the name of the Dark King, a line which turns everything on its head.]]

* YearInsideHourOutside: Time does not flow at the same pace in the Warp as it does in realspace. Argel Tal experienced six months in the Eye of Terror in ''The First Heretic'' while less than a minute passes outside.

'''Upcoming titles are:'''

* ''The End and the Death: Volume III'', by Dan Abnett

* Conscription: During the Siege of Terra, the defense is getting so desperate that civilians have to be drafted to be the first line of defense on the ground, as other more "precious" troops would be wasted manning the outer walls.

* AMillionIsAStatistic: In Prospero Burns, the Space Wolves drop [[spoiler:a Quietude graving dock onto the planet below]]. The Wolves' response: howl, shout, and shake their fists. The Imperial Army Leader's response: To chew out Leman Russ for destroying the electronic data and knowledge from the dock.

** In ''The End and the Death: Volume 1'', [[spoiler: Horus lists off the daemon forces in his service. Alongside the usual suspects such as Skarbrand, N'Kari and so on along with other Daemons from the Heresy, there's a veritable storm of names from other ''40K'' works including [[VideoGame/DawnOfWar Ulkair]], [[Literature/GreyKnights Ghargatuloth]], [[Literature/SoulDrinkers Abraxes]], [[Literature/{{Ultramarines}} M'kar]], and [[TabletopGame/BlackCrusade Ax'senaea]].]]

** The Blood Angels and White Scars practice fine arts, albeit less ostentatiously than the Emperor's Children.
* DarkMessiah: Horus (thanks to Chaotic manipulation) thinks that he is saving the galaxy by turning on the Emperor.
* DeadMansSwitch: In ''Old Earth'', the Emperor finally turns the Golden Throne into one after Vulkan inserts the Talisman of Seven Hammers (that the Emperor himself forged in Nocturne by commanding Vulkan's body) into its mechanism. If the Golden Throne fails or He dies, the Throne will engulf Terra in a roaring inferno, depriving Horus of the planet.

** In the ''The Burning of Ohmn-Mat'' PDF supplement for the tabletop game, a list of Aetheric Dominions for the Daemons of Chaos is given, rather curiously eight rather than the traditional five or six. While most of them map to the familiar Chaos powers (Heedless Slaughter to Khorne, Rapturous Sensation to Slaanesh, Infernal Tempest to Tzeentch, Putrid Corruption to Nurgle, Ravenous Dissolution to Malal/Malice), three new ones are included, with Samus's Aetheric Dominion changed from his Khornate alignment in the previous edition to the new Encroaching Ruin. [[spoiler: In ''The End and the Death: Part 1'', Samus is strongly suggested to be the herald of the Dark King, who corresponds to Encroaching Ruin as "the end and the death".]]

'''Euphrati Keeler:''' "For him, Nathaniel, because he can't. Today you and I have broken a brother's heart, and nothing will ever mend it."

* TheCavalryArrivesLate: Overlapping with YouAreTooLate. The Ultramarines, Dark Angels, and Space Wolves finally arrive at the Siege of Terra with sufficient numbers to decisively turn the tide in favor of the loyalists. By the time they get there, however most of the traitor primarchs have left or been banished, Horus and Sanguinius are dead, and the Emperor himself is mortally wounded. All that's left for them is to chase the remaining traitors away and start to pick up the pieces of the ruined Imperium.

** During the Battle of Pluto, the ''Phalanx'' itself, with Rogal Dorn aboard, comes to the rescue of the Imperial Fists patrols and Archamus' team who were trapped by the Alpha Legion. The Phalanx destroys the fleet and Rogal Dorn is able to kill Alpharius during this battle.
** In ''Wolf King'', the Vlka Fenryka is saved by a fleet of Dark Angels which helps defeat the Alpha Legion.

* CassandraTruth: At least three separate attempts are made to warn others about Horus's impending fall to Chaos. [[spoiler:Magnus' attempt destroys the Emperor's Webway project and gets the Space Wolves unleashed on Prospero, Eldrad's attempt gets the Maiden Worlds in the Perdus Anomaly virus-bombed by Fulgrim, and Leman Russ treats Eada Haelfwulf's dying words as Magnus' attempt to fabricate corroborating evidence]].
* CatchPhrase: For Numeon, "Vulkan Lives!" becomes a personal credo and war cry after Istvaan V.
* TheCavalry: During the Siege of Terra, the loyalists' hope is to hold until Roboute Guilliman and Lion El'Jonson arrive with their Legion to crush the traitors from behind. [[spoiler:Alas the interior wall is breached before the loyalists can arrive, which will lead to the Emperor teleporting aboard the ''Vengeful Spirit''.]]

** Averted by the World Eaters and Imperial Fists, who recruit from numerous cultures and therefore don't have a single dominant culture.
* CulturedWarrior: The Emperor's Children take this to the point of arrogance. The Thousand Sons as well--preserving libraries and knowledge (particularly of sorcery, but all subjects are considered important) is a primary goal to the point it brings them into conflict with the [[Literature/SpaceWolf Space Wolves]], and individual members have hobbies like philosophy and winemaking. Horus and his Mournival also fit the bill pre-corruption.
** The Blood Angels and White Scars practice arts, albeit less ostentatiously than the Emperor's Children.

** It is especially prevalent in ''Know No Fear''. As a result of the ''Campanile'' hitting the Calth Veridian Yard, the grand cruiser ''Antrodamicus'' drops out of low orbit and crashes into Kalkas Fortalice, killing thousands instantly. Then it goes to its LogicalExtreme when an orbital depot is destroyed and parked vehicles start falling out into atmosphere--and right above the Ultramarines 6th Company.

* DeathWorld: Many planets within the Imperium are utterly inhospitable to life, although it doesn't mean humans haven't managed to survive there. Some of the most famous are Fenris, an ice world where giant creatures roam everywhere; Caliban, whose forests are teeming with Chaos-corrupted monsters; and Baal, whose radioactive wastes are infested with mutants and predators. Not surprisingly, these worlds are perfect recruiting grounds for the Legions as the average inhabitant of a Death World is sure to be a prime candidate for becoming an Astartes.

** Millions of loyalist soldiers and civilians collectively hit their event horizon during the Siege of Terra. Some are driven mad, others desert, commit suicide, or flee for any refuge they can find.

The series began in 2006, and as of mid-2019, it consists of [[LongRunningBookSeries 38 novels, 103 short stories and novellas (some of which are collated in 21 anthologies), 47 audio dramas (plus 4 audio drama anthologies), 2 artbooks, 2 scriptbooks, and 1 graphic novel]]. ''The Primarchs'' sub-series (another 17 novels, 7 short stories, and 4 audio dramas) focuses specifically on the leaders of the Space Marine Legions. From 2019, the main series has officially been ended, and new works are being published as part of ''The Siege of Terra'' sub-series, focusing on the titular conflict and serving as a capstone to the overall series (7.5 of 8 novels released so far, plus 3 out of an unspecified number of planned novellas). The series is one of the Black Library's most popular, with new titles regularly appearing in ''The New York Times'' bestseller list.

** After Alpharius chases his Legion into the Alaxxes nebula and the Khan refuses to help, Leman locks himself up in his apartments aboard the Hrafnkel and doesn't come out until his second-in-command is getting ready for a Last Stand.

** The first novel, ''Horus Rising'', begins with the Sons of Horus storming the palace of the Emperor of Mankind and Horus personally slaying said Emperor. [[FakeOutOpening Said battle is revealed to merely be a minor engagement against a government that was coincidentally named like the Imperium of Man]]. The sequence introduces the Sons of Horus legion as well as Loken, one of the main characters of the book.
** ''Deliverance Lost'' starts in the later stages of the battle of Isstvan V with Corax and the Raven Guard beside him preparing for a last stand before they are evacuated by an allied fleet.
** ''Betrayer'' starts with the battle of Armatura, a combined Word Bearers and World Eaters assault on one of Ultramar's best defended worlds. How the XII Legion operates is presented through Kharn's eyes and highlights feature Lorgar tanking a Titan's fire and Angron lifting its leg.
** ''Ruinstorm'' begins on the Blood Angels being attacked by daemons while trying to cross the Ruinstorm while Guilliman's flagship is ambushed by a flotilla of traitor ships.
* ActionSurvivor: With all the citizens getting caught up in events, there are bound to be a few. One of the most notable is Euphrati Keeler, an imagist (photographer, in other words) of the Remembrancer Order who survived two separate daemon attacks, and even looks to be shaping up even further to being the first Imperial Saint.
* AfterTheEnd: The Horus Heresy era is essentially humanity rebuilding itself after its first interstellar empire collapsed thousands of years before. In the backstory, Earth had been rendered all but utterly inhospitable to life due to centuries of nuclear/chemical/biological warfare (with a little Chaos sorcery thrown in for good measure) during the isolation of the Age of Strife. If the Emperor hadn't shown up when he did, it most likely would have continued on and been left a burned-out lifeless rock (though he burned his share of places). Then we get to see all the OTHER human planets that went through cataclysmisms of their own during that time, never mind those that were completely obliterated ''on purpose.''

** The daemon that possesses [[spoiler:Kasper Hawser]] basically tells him this about the Thousands Sons and the Space Wolves' conflict.

** Some Primarchs were this way before they were rediscovered by the Imperium, due to just how different they were from vanilla humans. Some of those who would turn traitor were still suffering from this because of how they were radically different to the ideal that the Emperor had in mind for them, (e.g., the Night Haunter being a psychopathic terror tactician and Lorgar setting up churches to the Emperor).

* AmazonBrigade: The Sisters of Silence, composed entirely of women [[AntiMagic Blanks]], are one of the Emperor's exclusive elite strike force, usually used to investigate and take care of warp-related matters as their nature as blanks allow them to negate it.
* {{Ambadassador}}: Ambassador Vethorel, representative of Fabricator General Kane on the Council of Terra. In ''The Binary Succession'', the members of the Mechanicum are paralyzed because there are two Fabricator Generals they can follow, and are frustrated because of how the Imperium ignore these refugees. To save her people and prevent them from abandoning the Imperium completely, she successfully campaigns for the creation of an "Adeptus Mechanicus", which will sacrifice Mars' independance for more agency in the Imperium. Despite having enemies from all faction trying to off her, Vethorel survives and performs a remarkable feat of AggressiveNegotiations with the help of the Legio Titanicus (an Imperator Titan is piloted towards the Council), leading to the creation of said Adeptus and shaping the politics between Terra and Mars for the rest of the story.

* AndThenWhat: Touched upon in the first novel. Horus and Guilliman have decreed that all of their sons are to learn skills and knowledge unrelated to war, because he believes the Great Crusade has to end ''eventually'', and he wants his Astartes to have a place in the golden age that will follow. Things...don't turn out that way.
* {{Animorphism}}: Some Space Wolves "fall" and become Wulfen, who are essentially werewolves. Psyker and daemon abilities can force this change on a Space Wolf.

** Blunters, blanks, and pariahs, including the Silent Sisters, a military force composed entirely of female human blanks. All of these are resistant to the warp or even can negate its effects because of a rare genetic quirks. Several of these characters appear during the series and are a rare trump card against the occult.

** ''Galaxy in Flames'' has Horus virus-bomb Istvaan III, killing its entire population and ecology. Then he ignites the now-volatile atmosphere.

** In ''A Thousand Sons'', [[spoiler: Prospero is utterly destroyed by the Space Wolves.]]

* ArmyOfThievesAndWhores: Horus has many, many highly trained and disciplined mortal armies at his command, but the Traitors also make use of huge numbers of gangers, abhumans, and such.

** Throughout the series, Adeptus Mechanicus characters are shown wearing all sorts of extreme cyber-implants, as their faction sees this as a form of worship.

* AttemptedRape: InvokedTrope. In ''Fulgrim'', Serena D'Angelus makes this excuse to Lucius, lying that she murdered a remembrancer in self-defense because he was about to rape her. To really hammer in how the corrupted legion is falling in on itself, Lucius shrugs it off, telling her that he would send somebody in to clean up for her.

** Space Wolves wear hand-made leather clothing. They also drape tan wolf hides over their armor.

** [[spoiler: Another moment is in ''Mechanicum'' novel, when it's pretty much confirmed that the Machine God worshipped by the Mechanicum is actually Mag'ladroth, C'tan of technology, who was defeated by the Emperor in ancient times and imprisoned on Mars in order to inspire technological breakthroughs. Then the book with knowledge about containment was stolen, so he's likely to awaken in 42nd millennium...]]

** ''Galaxy In Flames'' is a ForegoneConclusion since it details the events that happened at the beginning of the Horus Heresy.
** ''Fulgrim'', since it details Fulgrim's [[FallenHero descent to Chaos]], and he manages to become [[VillainProtagonist the bad guy who won]]. He's the only Primarch that's flat out won in his every appearance. While every other Primarch is off fighting his own petty battles, Fulgrim gets the first [[spoiler:Primarch kill]] of the Heresy, fights off [[spoiler:the daemon who possessed him]], has the first legion to successfully convert to recognizable Chaos Marines, and [[spoiler: be the first to ascend to daemonhood]].
** ''Damnation of Pythos'' sees the daemons winning. The Grey Knights eventually cleanse the planet several centuries later in a different piece of canon entirely, but by that time the BigBad is long gone.

* BalkanizeMe: The Dark Angels homeworld of Caliban, under the command of Luther, ends up seceding from the Imperium amid the turmoil of the Heresy for a myriad of reasons, including but not limited to the extreme resentment of its garrison for being ReassignedToAntarctica, wide-spread hatred of the Imperium's destruction of Caliban's ecosystem and culture, and its defenders being slowly and subtly corrupted by the planet's inherent Chaos taint.

** After the Emperor's Children have gone into full insanity, the daemon possessing Fulgrim gets arrogant and starts slipping character in confidence that the Legionnaires are too far gone to notice or care. Despite the Emperor's Children becoming some of the most twisted and depraved traitors the galaxy has ever seen, the last thread of decency among them is that they are still loyal sons, and Lucius uses this to unify the captains into trying to rescue Fulgrim. [[spoiler: After they capture and torture Fulgrim to exercise the daemon, Fulgrim breaks free, and reveals to his sons that he managed to beat the daemon with his own HeroicWillpower some time ago. He was acting out of character because he wanted to see how far they would go, purely from a vain desire to have his sons demonstrate how loyal and dedicated they are to him ([[TooKinkyToTorture the potential pain was another great motivator]], but that's a different story). [[MasterSwordsman Lucius]] even catches on that the tiny hints that he could actually beat the thing wearing Fulgrim's body was just trying to goad Lucius into dueling him.]] Afterwards, the Emperor's Children aren't angry, but they [[AdmiringTheAbomination were actually impressed]] by the ploy.
* BattleCry: Pretty much every Legion's got one. The Space Wolves make snarls, roars and "leopard-growls" as well as "Hjolda Fenris!".
* BattleInTheCenterOfTheMind: An unusual case where [[spoiler: Kasper Hawser's]] mind was being altered by a [[spoiler: daemon]]. He couldn't fight the beast and he could only regain his memories by altering his dreams. [[spoiler: Space Wolf Rune Priests attempted to help him fight the being, but one of them was turned into a wolf. This priest claimed Horus turned evil.]] Later on, [[spoiler: Kasper walks through a room in Tizca and into the room that he is in in his dreams. The daemon combined the two realities.]] Therefore, it was a battle in the center of the mind outside of the body (where Space Wolves could run into his mind and shoot it). It took the arrival of [[spoiler: a Rune Priest, two dreadnoughts and two dozen Silent Sisters]] to beat it back.

** Garro, who imparted it unto Rogal Dorn, who imparted it unto the Emperor.

* BecauseDestinySaysSo: Curze lets his visions lead him and decide on his course of action.

* {{BFS}}: even considering that any given Astartes' or Primarch's sword is this to an ordinary human, Rogal Dorn and Leman Russ's favoured weapons are colossal.

** The battle of Isstvan V, or Dropsite Massacre, is one of the greatest battles in the Horus Heresy with eleven Legions being involved. It is first presented in ''Fulgrim'' where its main events are summarized, but following volumes will describe specific parts of it, from the Word Bearers' first engagement of the Gal Vorbak, to Corax trying to survive on the battlefield.
** ''Mechanicum'' features the start of the civil war between factions of the Mechanicum loyal to the Emperor and the separatists, with armies of Skitariis, entire Knight houses and Titan Legios being involved in the great war on Mars.
** ''A Thousand Sons'' describes the razing of Prospero, with the Vlka Fenryka coming on the eponymous planet to massacre its population. Prospero is defended by the Thousand Sons and the local militia, with the war climaxing with Magnus personally fighting Leman Russ in his own courtyard.
** ''Know No Fear'' narrates the entirety of the battle of Calth, from ground engagement between the Word Bearers and the confused Ultramarines to the space battles between the Word Bearers fleet and the remnant of Ultramar's fleet.
** ''Fear to Tread'' ends on the entire Blood Angel Legion engaging a host of daemons of Khorne and Slaanesh, Sanguinius pitting himself against Ka'Bandha, one of Khorne's most powerful Bloodthirsters.
** ''Master of Mankind'' features the final battle of the War Within the Webway, with a host of daemons assaulting the ruins of an Eldar city held by the Legio Custodes and Silent Sisters, supported by a host of skitariis and a Titan Legio. The Emperor himself steps into the fray and demonstrates his might by engulfing a whole section of the Webway with psychic flames that destroy most of the daemons.
** The Siege of Terra books are an entire series of this, featuring void battles in which entire moons are blown up and space hulks are used as fire ships,continent-spanning trench warfare, rampaging hordes of daemons and beastmen, brutal close-quarters fighting beneath the Palace walls, primarchs fighting primarchs and greater daemons, Titan legions waging battles of mutual annihilation, gigantic siege engines rigged with supersized sonic weaponry, aerial duels between hundreds of fighters at a time, and orbital bombardments that are so intense that they ''shift the planet's tectonic plates''.

** Horus performs one during the battle of Sixty-Three Nineteen, when he teleports into the throne room of the local "Emperor" who has activated a DoomsdayDevice, and both kills the Emperor and deactivates the device in a single shot, which saves Garviel Loken.
** During the Battle of Calth, Guilliman is blown into space by a Word Bearer salvo but later reappears to save Thiel and his men from a being killed by a boarding party of Word Bearers. As it turns out, his flagship ''Macragge's Honour'' is big enough to trap a thin atmospheric envelope around its hull, and Guilliman's transhuman constitution allows him to breathe in it.

** In ''Old Earth'', Vulkan participates for a grand total of one minute in the battle of the Aragna Chain, when he teleports into the vessel ''Horus Triumphant'' to smash apart a Contemptor Dreadnought that was about to kill the Salamander Nuros and his boarding party.

** ''Flight of the Eisenstein'': The ''Eisenstein'' with Garro and his companions within manage to warn Rogal Dorn and Malcador the Sigillite about Horus' betrayal. On the other hand, many of them are now detained indefinitely, and the youngest Astartes of the group is corrupted by Chaos and must be put down by Garro.
** ''Descent of Angels'': Zahariel manages to save Lion El'Jonson from a bomb, but is blamed alongside Luther and is ignominiously sent back to Caliban supervising recruitment.

** In a ForegoneConclusion sort of way, the entire series is this -- Horus is slain, the Heresy is ultimately thwarted as his forces retreat, and the Imperium lives to fight another day, but the Emperor has been placed on life support, the galaxy is doomed to face a gauntlet of conflicts over the next several thousand years that will lead to untold trillions of deaths, and the forces of Chaos gain a lot of new supporters as the Chaos Gods become more powerful.

** In the short story ''Serpent Beneath'', Omegon orders a strike force of Alpha Legionnaires to attack one of the legion's own secret black sites, which is dedicated to the study of a strange artefact which may be a Black Pylon, the containment of psykers and is used to stall the White Scars.

** Eada Haelfwulf and Ulvurul Heoroth, AKA, Longfang in Prospero Burns. Also, Thousand Son Astartes and [[spoiler: the daemon]] bleed from the mouth, well as other orifices, when confronted with powerful marks of aversion and pariahs.

** In ''A Thousand Sons'' after [[spoiler:a Thousand Son succumbs to the flesh-change and accidentally kills a Space Wolf]] Leman Russ swears a BloodOath that there will be a reckoning between him and Magnus.

* BodyguardBetrayal: A cruel example in ''The End and the Death''. When the Emperor teleports into the Vengeful Spirits, his [[spoiler:own Custodes bodyguards]] attack him, being overcome by Chaos. This even manage to anger the Emperor because [[spoiler:the Custodes]] were His companions, and not just his soldiers.

* BringNewsBack: In ''The Flight of the Eisenstein, Garro and his surviving comrades aboard the eponymous cruiser must cross the galaxy to reach Terra and warn the Imperium of Horus' treachery at Istvaan III.

** The Emperor himself, for those gifted with psyker sight. He's so powerful, looking at him causes SensoryOverload, and one character has a panic attack even remembering this. It partly bleeds over to the mortal world -- most people can't stand looking at the Emperor directly when he's not masquerading. The only people unaffected by this are the Primarchs and Malcador.

* CainAndAbel: Rather than a single case, it's essentially half a fraternity of {{Physical God}}s becoming the Cain to the other half's Abel. There are also specific cases between individual Primarchs. Most notably, Perturabo is the Cain to Dorn's Abel; then there's Russ, the ''loyalist'' Cain to Magnus's Abel.

* CameBackWrong: Erebus brings back [[spoiler: Cyrene]] with much agoniser screaming, and the process makes her a Perpetual.

* CapturedOnPurpose: In ''Deathfire'', the Unburdened Xenut Sul lets himself get captured by Ultramarines to infiltrate Maccrage and try to kill Barthusa Narek.

** During the Battle of Pluto, the ''Phalanx'' itself, with Rogal Dorn aboard, comes to the rescue of the Imperial Fists patrols and Archamus' team who were trapped and attacked here by the Alpha Legion. The Phalanx destroys the fleet and Rogal Dorn is able to kill Alpharius during this battle.

* CavalryBetrayal: The Drop Site Massacre at Isstvan V, one the most significant and shocking battles of the Horus Heresy. The Raven Guard, Salamanders and Iron Hands were pitted against the Sons of Horus, Emperor's Children, Death Guard and World Eaters. The three loyalist legions expected reinforcements from the Alpha Legion, Night Lords, Iron Warriors, and Word Bearers, but these four legions had already joined Horus' side. When the Salamanders and Raven Guard fell back on the new arrivals, they were engulfed in a hurricane of fire that devastated their numbers in moments. The resulting bloodbath resulted in one of the worst defeats for the Imperium. The three loyalist legions were reduced to no more than 22,000 Astartes. Ferrus Manus was killed by Fulgrim, becoming the first primarch to fall on either side, while Vulkan disappeared after the Iron Warriors fired a tactical nuke at him.

* TheCavalry: During the Siege of Terra, the loyalists' hope is to hold until Roboute Guilliman and Lion El'Jonson arrive with their Legion to crush the traitors from behind. [[spoiler:Alas the interior wall is breached before the loyalists can arrive, which will lead to the Emperor teleporting aboard the Vengeful Spirit.]]

* CombatByChampion: Used to settle inter-Legion disputes ''in extremis'' during the Crusade and after the Heresy. Sigismund and Alajos converse during one such disagreement, anticipating that they will be designated champions for their respective Legions.

* Conscription: In Terra, the defense is getting so desperate that civilians have to be drafted to be the first line of defense on the ground, as other more "precious" troops would be wasted manning the outer walls.

** In ''Nemesis'' Siress Callidus wants to deploy a new Callidus assassin to kill Horus. The assassin's name? M'shen, the woman who assassinated Konrad Curze.

** In ''The End and the Death: Volume 1'', [[spoiler: Horus lists off the daemon forces in his service. Alongside the usual suspects such as Skarbrand, N'Kari and so on along with other Daemons from the Heresy, there's a veritable storm of names from other ''40k'' works including [[VideoGame/DawnOfWar Ulkair]], [[Literature/GreyKnights Ghargatuloth]], [[Literature/SoulDrinkers Abraxes]], [[Literature/{{Ultramarines}} M'kar]], and [[TabletopGame/BlackCrusade Ax'senaea]].]]