The Heresy came to Calth without warning. In just a few hours of betrayal and bloodshed, the proud warriors of the XIIIth Legion - Guilliman's own Ultramarines - were laid low by the treachery of their erstwhile brothers of the XVIIth. Now, as the planet is scoured by solar flares from the wounded Veridian star, the survivors must take the fight to the remaining Word Bearers and their foul allies, or face damnation in the gloomy arcology shelters beneath the planet's surface.

The Shadow Crusade has begun. While the Ultramarines reel from Kor Phaeron's surprise attack on Calth, Lorgar and the rest of the Word Bearers strike deep into the realm of Ultramar. Their unlikely allies, Angron and the World Eaters, continue to ravage each new system they come across - upon the garrison planet of Armatura, this relentless savagery may finally prove to be their undoing. Worlds will burn, Legions will clash and a primarch will fall.

In the wake of the Dropsite Massacre at Isstvan V, the survivors of the Salamanders Legion searched long and hard for their fallen primarch, but to no avail. Little did they know that while Vulkan might have wished himself dead, he lives still...languishing in a hidden cell for the entertainment of a cruel gaoler, his brother Konrad Curze.

From the battlefields of Phall and Isstvan, to the haunted shadows of Terra itself - the greatest war in the history of mankind rages on. While the traitor Legions continue their campaign of terror across the galaxy, preparations are made for the defence of the Imperial Palace and the final, inevitable reckoning that must yet come between Horus and the Emperor....

Far out on the Eastern Fringe, the realm of Ultramar stands alone. Having weathered the Word Bearers' attack on Calth and the subsequent Shadow Crusade against the Five Hundred Worlds, the Ultramarines primarch Roboute Guilliman now draws all loyalist forces to Macragge as he contemplates a new future for mankind.

Once the brightest star in the Imperium and always first among his primarch brothers, Horus has dragged the Space Marine Legions into the bloodiest conflict that the galaxy has ever seen. While their allies wage war on a thousand different fronts, the XVIth Legion descend upon the Knight world of Molech - home to the ruling House Devine, and a principle stronghold of the Imperial Army.

Since the earliest days of the Great Crusade, Sanguinius - angelic primarch of the IXth Legion - was ever among the closest and most loyal of Horus' brothers. But the Blood Angels have long kept their true nature hidden from the rest of the Imperium, and when the Warmaster hints that the key to their salvation may lie in the ruins of a conquered world, the sons of Sanguinius race to claim it.

In the aftermath of the Dropsite Massacre at Isstvan V, a battered and bloodied force of Iron Hands, Raven Guard and Salamanders regroups on a seemingly insignificant death world. Fending off attacks from all manner of monstrous creatures, the fractious allies find hope in the form of human refugees fleeing from the growing war and cast adrift upon the tides of the warp.

Vulkan lies in state beneath the Fortress of Hera, and yet many of his sons still refuse to believe that he is truly dead. After a seemingly miraculous rescue by the Ultramarines, Artellus Numeon, once captain of the Pyre Guard, urges the other Salamanders on Macragge to leave Imperium Secundus and return their primarch's body to the home world of Nocturne - there to be reborn in the flames of Mount Deathfire.

Created in the Emperor's own image, the primarchs had long thought themselves to be princes of the universe and masters of their own destiny - they led the Space Marine Legions in glorious conquest of the galaxy, and no enemy of the Imperium could stand against them. However, even amongst this legendary brotherhood, the seeds of dissent had been sown long before the treacherous Warmaster Horus declared his grand heresy.

Only from out of great conflict can true heroes arise. With the galaxy aflame and war on an unimaginable scale tearing the Imperium apart, champions of light and darkness venture onto countless fields of battle in service to their masters. They ask not for remembrance or reward - simply to meet their destiny head-on, and only by embracing that destiny will they come to learn what the unseen future may yet hold for them....

For long years, the Horus Heresy has ground on. Now, the Death Guard have been sent to begin the final battle. But Mortarion and his sons must face their gravest challenge first - for Nurgle has claimed them as his own, and he will not be denied.... The skies darken over Terra as the final battle for the Throne looms ever closer.... As the Traitor primarchs muster to the Warmaster’s banner, it is Mortarion who is sent ahead as the vanguard of the Traitor forces. But as he and his warriors make way, they become lost in the warp and stricken by a terrible plague. 

After the horrors of Istvaan V, Horus declares outright war against the Imperium. In the shadows of the Emperor's Palace, powerful figures convene. Their plan is to send a team of assassins to execute the arch-traitor Horus and end the war for the galaxy of mankind before it's even begun. But what they cannot know is that another assassin is abroad already, with his sights firmly set on killing the Emperor.

The Emperor's vision of mankind ascendant lies in tatters. The Great Crusade is naught but a fading memory. The dream of Unity is no more. But with Horus's rebellion spreading to every corner of the Imperium and war engulfing new worlds and systems almost daily, there are some who now ask: were the signs there to be seen all along?

As the Horus Heresy divides the Imperium, Corax and his few remaining Raven Guard escape the massacre at Isstvan V. Tending to their wounds, the bloodied Space Marines endeavour to replenish their numbers and return to the fray, taking the fight to the traitor Warmaster.