Three primarchs have forged an uneasy alliance to create a bastion against the death of their father’s empire: Imperium Secundus. A practicality for some, a beacon of hope for many and outright treason for others.

Isolated from the wider war by the Ruinstorm, Roboute Guilliman is hard pressed to maintain stability and safety of his new order in the face of attacks from within and without as well as tensions between the triumvirate of primarchs at its head.

While Lion El’Johnson keeps getting into conflict with his brother-primarch about his methods and morals, his distant homeworld faces even more upheaval. Amongst the Dark Angels left behind to garrison Caliban, a powder keg of allegiances, politics and shadow plays is close to be lit into outright flames. In the wake of the fire, the future of the Legion will be decided by what rises from the ashes.

The third member of the triumvirate, Sanguinius of the Blood Angels, is trying to accept his appointed role as Imperator Regis, but is still being plagued by grim visions of his coming demise at the hands of Horus Lupercal. What will the Angel do when he seems to become strangled both by the demands of his role in their young empire and by the strands of fate itself?

In the final days of Imperium Secundus, all three primarchs have to face both the daemons of their souls and the creatures of the Warp on a journey through madness and mortal danger…

In direct contrast to all the fuss with its “Preludes”, the actual Imperium Secundus-stories are as straight-forward as it gets. Because the Imperium Secundus is isolated from the rest of the galaxy by the Ruinstorm, no new characters arrive and no one moves away to have crossovers elsewhere. There’s a clear time-line and the four novels of the story-arc follow a linear sequence of events.

The Unremembered Empire sees the arrival of the relevant players and the founding of Imperium Secundus. Pharos is about the battle for the titular lighthouse. Angels of Caliban sees the triumvirate of Guilliman, the Lion and Sanguinius tested almost to a breaking point, while the developments on Caliban reach a critical mass. Ruinstorm closes the arc and is about disbanding and leaving Imperium Secundus again. This Omnibus contains the latter half of the story, anchored around Angels of Caliban and Ruinstorm.

Peppered in between the four novels are a lot of short-stories that give context and expand on some characters. Most of these have already been included in I: Hope’s Kindling, but II: Fate's Ashes also contains a few noteworthy shorts which are about the Dark Angels (Cypher Guardian of the Order, Master of the First, Exocytosis) and a particular Night Lord (The Long Night). I leave it to you to discover how Sermon of Exodus fits into the stories of the omnibus.

The two closing stories from this omnibus, Spear of Ultramar and Dreadwing, are two novellas (so far only available as eShorts) that are each an epilogue to the stories of Guilliman and the Lion respectively after they leave the closing page of Ruinstorm. If you want an additional extension to the epilogue of the story of Guilliman and the XIIIth Legion within the Horus Heresy, you could read the Primarchs-short story The Atonement of Fire (not listed in the reading order above) as a bonus story that further expands on the themes of Spear of Ultramar. Those stories close the series-long arcs for two thirds of the triumvirate of Imperium Secundus, leaving them in the positions that they’ll probably stay in until The Siege of Terra reaches its conclusion.

In addition to the second half of the story of Imperium Secundus, this Omnibus also contains the second half of the story of Caliban and the Dark Angels abandoned there. Luther, Zahariel and other mistrusted Legionnaires have been isolated there by the Lion since all the way back in Descent of Angels (see Angels of Darkness). During all this time; the planet has become a melting pot for hidden corruption and secret agendas, reaching a boiling point in Angels of Caliban.

The true climax to the Dark Angels’s story - the Lion returning to Caliban, the discovery of Luther’s rebellion and the subsequent battle - has yet to be covered in novel form by Black Library. If you’re eager for more, I’ve listed some recommendations for further reading about the Dark Angels below and back on the omnibus page of Angels of Darkness. Notable in that regard are especially the novels Angels of Darkness and Luther: First of the Fallen (see below), both by Gav Thorpe, which see Astelan and Luther respectively being interrogated by present-day-Dark Angels about the bygone times of the Heresy.

Konrad Curze: The Night Haunter by Guy Haley is one of the Primarchs books that employ a more subjective approach to their subject. The framing device of the book takes place a good while after the end of the Heresy, with the Night Haunter sifting through his shattered psyche across the memories of his lifetime. It's a more experimental approach to this kind of novel, which is as dark as you can expect. I recommend reading this only after you've finished Curze's arc in the Heresy in Imperium Secundus II: Fate's Ashes. Here's Guy Haley talking about The Night Haunter.

Luther: First of the Fallen by Gav Thorpe from the Horus Heresy Characters range is somewhat similar to The Night Haunter in that it looks at a Heresy-era character through his own eyes and words in retrospect from after the end of the Heresy. Specifically, the framing device of Luther has him imprisoned after his failed attempt at rebellion on Caliban and over the span of ten thousand years successively interrogated by different generations of Dark Angels. The book is almost a spiritual sequel to Gav's earliest Dark Angels work, Angels of Darkness (2006), which had introduced the narrative device of imprisoned-Fallen-tells-subversive-account-of-the-events-of-the-Heresy. Here's Gav Thorpe talking about First of the Fallen.

This is the direct sequel to Imperium Secundus I: Hope's Kindling.

If you’ve been following this reading order, you should have already read the "Prelude to Imperium Secundus"-Omnibuses and are up-to-date with the story-lines presented here. If you haven’t followed along with the “Preludes”, here’s a quick primer: the first third of the Ultramarines’ story is being told in Shadow Crusade I: Only the Faithful. The first third of the Dark Angels’ story is presented in Angels of Darkness. The first third of the Blood Angels’ story is part of Shadow Crusade III: Chosen of Chaos.

This is the closing chapter to the story of the Ultramarines and the Dark Angels.

The final part of Sanguinius’ story this side of the Siege can be found in the closing Omnibus Shadow of the Warmaster IV: The Dead and the Dying.

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:

• Dark Imperium-trilogy by Guy Haley, starting with Dark Imperium

  • This series tolled the bell for the start of the literary adaptions of "New40k", the times after the massive upheavals of the events of The Gathering Storm, which shifted the "modern" timeline a few centuries forward and included the opening of the Great Rift, the rise of the Aeldari God of the Dead and...the return of Roboute Guilliman to the 41st millenium. The first novel of the trilogy connects neatly with the end of Guilliman's arc in this omnibus, as Dark Imperium starts with the events that led to Guilliman's demise after the end of the Heresy and then jumps foward into the future after his reawakening
  • The trilogy was recently re-published to realign with certain adjustments to the timeline; here's Guy Haley talking about the final novel Godblight, the trilogy as a whole and the changes in the re-published books (beside the fancy new covers); he also talked on Twitter about it