Omnibus cover image

The Story

Death. There could be no other judgement for the Legion of Roboute Guilliman in the court of the traitors. While other Legions and primarchs were tried to be lured, coerced or manipulated into the Warmasters' fold, Horus and his high-priest Lorgar marked the Ultramarines out for destruction.

Their end is planned to come about through the dagger to the back, struck down in surprise by a seeming ally on the planet of Calth. Ignorant to the Warmaster's plans for rebellion, the Ultramarines are called there to attend a great mustering at the side of the Word Bearers.

Despite or because of a history of bad blood between them and the sons of Lorgar, the Ultramarines dutifully embrace the opportunity to build new bonds with their estranged siblings. But soon the masks fall, the clocks strike zero, and Guilliman and his Legion find themselves in the charnel house of the most bitter, desperate and long-lasting battle of their history: the Underworld War…

Reading Order

Legend: Novels; Novellas (anthology); Short Stories (anthology)
  1. The Shards of Erebus (MoC)
  2. Know No Fear
  3. Calth That Was (MoC)
  4. Dark Heart (MoC)
  5. The Traveller (MoC)
  6. A Deeper Darkness (MoC)
  7. The Underworld War (MoC)
  8. The Honoured (eShort)
  9. The Unburdened (eShort)
  10. Censure (LoB)
  11. Athame (MoC)
  12. Unmarked (MoC)
  13. Macragge's Honour
  14. Children of Sicarius (HotS)

Censure and Children of Sicarius were originally produced as audio dramas and only later re-published as short stories in prose format.

While The Honoured and The Unburdened are listed as "eShorts", they are in fact not short stories, but novellas (or short novels), just ones that are only available as stand-alone eBooks and not as part of an anthology.

Macragge's Honour is a graphic novel that's currently only available online.

Why this Reading Order?

Turns out there are a lot of stories written about the Battle of Calth. Taken together, there's not a single theatre of war in the annals of the Heresy this side of the Siege with as much coverage in the books: one novel, a dedicated anthology of short-stories, a pair of complementary novellas, at least one audiobook and the only graphic novel of the Heresy (more on that later). All paint a vivid picture of the Word Bearers' surprise attack on the Ultramarines, the long-winded aftermath in the form of the Underworld War beneath the surface of Calth as well as adjacent battles. And, to be honest, it's pretty cool overall. Know No Fear is an excellent novel and Mark of Calth a great example for how well a clearly themed anthology can come together.

Remus Ventanus & Maloq Kartho

The Battle of Calth is also, apart from the core conflict detailed in Know No Fear, a quite isolated event. After the initial apocalyptic fighting, both the Word Bearers and the Ultramarines basically leave behind parts of their Legion to wipe each other out while the rest of their forces and their primarchs move on to pursue the war elsewhere. Lorgar is at the head of the Shadow Crusade ravaging across the Ultramar system (see Shadow Crusade III), while Guilliman is busy defending said system and establishing the foundations of Imperium Secundus (more on that in Imperium Secundus I).

That is why this Omnibus is presented as an optional detour between Shadow Crusade I and III: you can visit it if you're interested in the Extended Edition of the Battle of Calth ("Bigger! Longer! Uncut!"), but for continuity's sake are also fine if you skip it as long as you've read Know No Fear.

The backbone of this omnibus are Know No Fear and the anthology Mark of Calth. If you want to keep things straight and simple, you can just get these two and receive a pretty extensive version of the Battle of Calth. The anthology has an additional treat for those that read it as one book instead of reading the included stories piece-meal as eShorts: short, little intermissions between the short stories in the anthology - quotes, distress calls, mission reports and other small snippets that add texture to the planetary catastrophy that is the surprise war on Calth. To my knowledge, Black Library didn't do anything similar with other anthologies, which is a shame. Still a cool feature of MoC.

Blue versus Red: Sergeant Kiuz Selaton versus a warrior of the XVIIth

Apropos Know No Fear: I am of course aware of the fact that Know No Fear is already collected in the Omnibus that directly preceded this one. It might seem repetitive and superfluous to include the same novel both at the end of Shadow Crusade I and at the beginning of II. The reason for this is my self-set goal that every Omnibus should succeed on two standards, a two-fold goal that mirrors the task the authors had when writing the novels themselves: every installment should work as a piece of the wider puzzle of the series, but should also tell a satisfying story of its own.

So while I give all those instructions about required reading, fitting follow-ups and the whole flow-chart with good reason, I think the Omnibuses should also be worthwhile reads if picked up out-of-order. So if a reader has heard about the Battle of Calth or is just very interested in the Ultramarines and/or Word Bearers, they might decide to just jump straight into Underworld War without bothering with Only the Faithful or any other Omnibus. I'd like to make it worth their while, and you really can't have a Battle of Calth Omnibus without Know No Fear.

For anyone following the Omnibus Map that has already read Shadow Crusade I, they can just ignore Know No Fear's second inclusion and go straight for the short-stories from Mark of Calth.

Added to the novel and the Calth-anthology Mark of Calth are five "bonus stories": two short-stories from other anthologies, duology of novellas and the aforementioned graphic novel.

The Honoured and the Unburdened: Steloc Aethon & Kurtha Sedd

The two short stories, Censure and Children of Sicarius, basically act as epilogues to some hanging threads from the other stories - more on Sicarius below. The two novellas (or short novels, depending how you want to look at it) The Honoured and The Unburdened were originally released together as an anthology alongside the release of the 'Betrayal at Calth' box set for the tabletop game. While neither game set nor anthology are regularly for sale anymore, the novellas have since been made available individually as eBooks.

Marius Gage & Kor Phaeron

Now a few words on that graphic novel: Did you know that there's a Horus Heresy comic book? It's called Macragge's Honour and is written by no one else than Dan Abnett and illustrated by Neil Roberts, the artist responsible for the Horus Heresy cover art. It's a direct sequel to a hanging thread from Know No Fear and tells the story of the space battle between the flagships "Infidus Imperator'' and "Macragge's Honour", which was teased at the end of Know No Fear as "one of the most infamous naval duels in Imperial history". Sounds like a match made in heaven, right? I personally haven't read Macragge's Honour myself and can't say anything about its quality, but at least from a publishers standpoint the experiment doesn't seem to have paid off: to this day it remains the only Horus Heresy publication in comic book format. It's nowadays difficult to come by a copy of it, as Games Workshop has stopped printing and selling the physical edition, but it's still available as an eBook on (and you never know what you can find second-hand on eBay).

The last story of this Omnibus is a regular short-story again and is basically an epilogue to the events of the graphic novel. Children of Sicarius was originally released as an audio drama and takes a look at the disciples of Kor Phaeron as they arrive on the daemonic planet Sicarius in the aftermath of the conclusion of the battle between the two ships. If you just don't fancy reading a comic book, you could also just skip Macragge's Honour and read Sicarius as an epilogue to the Omnibus as a whole.

Additions from 'The Primarchs' & 'Horus Heresy Characters'

If you haven't, you could read Roboute Guilliman: Lord of Ultramar or Lorgar: Bearer of the Word (see Only the Faithful) which expand upon the backstory of the primarchs of the XIIIth and XVIIth.

Required and Recommended Reading

As explained above, this is an expansion of the events from Shadow Crusade I: Only the Faithful. It fits naturally between this and the third part of the Shadow Crusade trilogy, III: Chosen of Chaos

As this includes every story about the Battle of Calth, you could also theoretically read this directly after the opening Omnibus Heresy Rising. You would then just miss out on the context that the stories from Shadow Crusade I (that aren't Know No Fear) provide.


The direct sequel to this is Shadow Crusade III: Chosen of Chaos. It shows, among other things, what the rest of the Word Bearers were up to while the Underworld War raged on.

Shadow Crusade I-III, Anvil of War and Angels of Darkness are the three narrative threads that together form the “Prelude to Imperium Secundus”. When one has read all of them, one is ready to read the Imperium Secundus-arc beginning with Imperium Secundus I: Hope’s Kindling. Many characters from Underworld War will make another appearance somewhere along that road.

The story of Oll Persson will see another pre-Siege continuation in the late-stage Omnibus Through the Neath.

Required Books

Novels (in order of appearance)

  1. Know No Fear
  2. Macragge's Honour

Anthologies (in order of appearance)

  1. Mark of Calth (MoC)
  2. Legacies of Betrayal (LoB)
  3. Heralds of the Siege (HotS)

Novellas (in order of appearance)

  1. The Honoured (eShort)
  2. The Unburdened (eShort)

A note on anthologies: Listed above alongside the respective novels are those anthologies that together contain every short-story and novella listed in the Reading Order of this Omnibus. Instead of buying whole anthologies, you could also buy any of the individual stories of the Reading Order as an individual eBook. The price per story is higher when buying individual eBooks compared to buying them as part of an anthology.

Beyond the Heresy

The following are recommendations from other series and the wider Black Library canon. If you are interested in the characters, factions or themes that were part this omnibus, the following books might also be to your liking.

Books from the 41st millenium

  • Calgar's Siege and Calgar's Fury by Paul Kearney

    • These two novels are about the deeds of Marneus Calgar, acting Chapter Master of the Ultramarines in the 41st millenium, who wears the fists of Guilliman into battle. If you're eager for more righteous fury doled out by the sons of Guilliman, look no further

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