It is the 31st millennium. Under the benevolent leadership of the Immortal Emperor, the Imperium of Man hasstretched out across the galaxy. It is a golden age of discovery and conquest. But now, on the eve of victory, the Emperor leaves the front lines, entrusting the great crusade to his favourite son, Horus. Promoted to Warmaster, can the idealistic Horus carry out the Emperor's grand plan, or will this promotion sow the seeds of heresy amongst his brothers?

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.

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.

As the Indomitus Crusade begins, fleets of mighty warships leave Terra on a vital quest to stabilise Imperium Sanctus in the wake of the Great Rift. The returned primarch, Roboute Guilliman, leads a huge force towards the shrine world of Gathalamor, where stable warp routes will allow the flotilla to spread across the beleaguered southern half of the Imperium.

Before the being called the Emperor revealed himself, before the rise of the aeldari, before the necrontyr traded their flesh for immortal metal, the world was born in violence. Even when they inhabited bodies of flesh, Trazyn the Infinite and Orikan the Diviner were polar opposites. Trazyn, a collector of historical oddities, presides over a gallery full of the most dangerous artefacts - and people - of the galactic past. Orikan, a chronomancer without peer, draws zodiacs that predict and manipulate the future.