On the 13th day of Secundus, the bombardment of Terra began. With the solar defences overcome through the devastating strength of the Traitor armada and the power of the warp, Horus launches his assault on the Throneworld in earnest. After withstanding a ferocious barrage of ordnance, an immense ground war commences outside the Palace, with every inch gained paid for in the lives of billions. 

The Traitor Host of Horus Lupercal tightens its iron grip on the Palace of Terra, and one by one the walls and bastions begin to crumple and collapse. Rogal Dorn, Praetorian of Terra, redoubles his efforts to keep the relentless enemy at bay, but his forces are vastly outnumbered and hopelessly outgunned. Dorn simply cannot defend everything. Any chance of survival now requires sacrifice, but what battles dare he lose so that others can be won? Is there one tactical stroke, one crucial combat, that could turn the tide forever and win the war outright? 

After seven years of bitter war, the end has come at last for the conflict known infamously as the Horus Heresy. Terra now lies within the Warmaster’s sights, the Throneworld and the seat of his father’s rule. Horus’ desire is nothing less than the death of the Emperor of Mankind and the utter subjugation of the Imperium. He has become the ascendant vessel of Chaos and amassed a terrible army with which to enact his will and vengeance. But the way to the Throne will be hard as the primarch Rogal Dorn, the Praetorian and protector of Terra, marshals the defences.

After a series of victories, the Imperial forces are on the back foot once more. The power of Chaos is rising, the Traitors gain ground, and all hope seems lost. Can Terra endure? 

The Inner Walls are breached. Traitor vanguards tear towards the heart of the Palace, sensing victory. Desperate gambits are attempted: an unwilling saint is released into the ruins, as well as an enthusiastic sinner. A black sword rises, forged from spite, ready to create a legend. But amid the slaughter, Jaghatai Khan, Warhawk of Chogoris, prepares to launch the most audacious strike of the conflict. His goal is nothing less than the liberation of the Lion's Gate space port. 

Of all the Emperor’s sons who fell to Chaos, it is perhaps Magnus the Red whose tale is the most tragic. Sanctioned because of his desire for knowledge, chastised, judged, and shattered to his very elements – there is much for the Crimson King to feel vengeful for. Yet revenge is not the only thing that draws him to Terra alongside the Warmaster’s besieging armies. He seeks something, a fragment, the missing piece of himself that lies within the most impregnable place on the planet – the inner sanctum of the Imperial Palace.

Horus’ armada gathers, and he has defeated all enemies sent against him, even the Emperor’s own executioner. One barrier remains before he can strike for Terra and lay waste to the Emperor’s dream. The Beta-Garmon system occupies the most direct and only viable route to the Solar System and Terra. To break it, Horus assembles a war host of incredible proportions and Titans in untold numbers. To lose here is to lose the war, and Horus has no intention of turning back. But the Imperium understands the importance of Beta-Garmon too. 

The Shattered Legions crew of the Sisypheum, broken and at the end of their endurance, find themselves divided - torn between following their resurrected captain on a suicidal mission or obeying orders to return to Terra and rejoin their Legion brothers. Following a series of garbled messages intercepted by the Kryptos, the divided warriors descend to the shattered surface of Luna. Here, their bonds of loyalty, duty, and their devotion to one another will be tested as ancient horrors of the earliest days of gene-manipulation are unleashed, and a long-buried secret is revealed.

After a long and gruelling conflict, the traitors at last close upon Terra. But time is dwindling for an attack. Both Guilliman and the Lion are returning with all haste, and their armies could turn the tide. The hosts of the Warmaster must unite, for only then can they attack the Throneworld itself. While Mortarion is sent on ahead as the fleet’s vanguard, it falls to Lorgar and Perturabo to marshal Fulgrim and Angron, both now elevated to daemonhood and perhaps beyond even the will of the Warmaster to command.

The Sabbat War is a savage Imperial crusade, cutting a bloody, burning path across a vast swathe of the Imperium's lost territory. On the front line, the stalwart regiments of the Astra Militarum, including the valiant Tanith First-and-Only—better known as Gaunt’s Ghosts—confront the relentless menace of Chaos, the Archenemy of Mankind. There is, and ever will be, only war.

Imperium Secundus lies revealed as a heretical folly. Terra has not fallen, though it remains inaccessible. Sanguinius, Guilliman and the Lion El’Johnson, the primarchs of the Triumvirate, must reach Terra at all costs. They seek to defend the Emperor and to atone for their sins. But the Ruinstorm, a galaxy-wide maelstrom of chaos, hides the Throneworld from the primarchs. Now the fleets of three Legions depart Macragge, and the primarchs will stop at nothing to overcome the Ruinstorm.

Removed from the concerns of the galaxy at large and regarding the Warmaster's unfolding Heresy with cold detachment, he has dedicated his hollow existence to the preservation of all the knowledge once held in the great libraries of Tizca, should mankind ever seek such enlightenment again. But his sons can see the change in their primarch - he is a broken soul whose mind and memories are slipping away into the tumult of the warp.

The Indomitus Crusade continues its war across the stars. The primarch Roboute Guilliman has finally broken through the orkish threat bedevilling the sectors near Fenris, and makes ready to push on his bid to stabilise the Imperium Sanctus—but old and bitter foes stand in his way. Kor Phaeron, the Dark Cardinal, threatens the previously stable core of the Segmentum Solar. Waves of rebellion instigated by his infiltrating priests suggest an imminent, large-scale invasion by the Word Bearers Legion. 

A galaxy burns and brother turns on brother as the conflict brought about by a beloved son’s betrayal reaches its fateful end. The Warmaster Horus has triumphed. His massive fleet at last nears Terra and the patriarchal Throne of his hated father. Many have fallen to bring this moment about; their tales are the ashes upon which the Heresy was born and prospered. Others have played their own small parts, drops in an ocean of war and blood. None of it matters. Terra looks to the skies as it raises its defences. Armies muster, heroes raise their swords, citizens cower. The war is coming. And nothing can stop it.

While Horus' rebellion burns across the galaxy, a very different kind of war rages beneath the Imperial Palace. The 'Ten Thousand' Custodian Guard, along with 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, infested by daemonic entities after Magnus the Red's intrusion.