The Imperium stretches across countless worlds, a newborn empire on the brink of ultimate victory. Yet at the peak of this golden age of conquest, the galaxy has been plunged into an Age of Darkness. Horus Lupercal, Warmaster of the Emperor's armies, has turned against his gene-father – and the eighteen Space Marine Legions, once united in a Great Crusade to consolidate all humanity beneath the Emperor’s banner, are riven by betrayal. This is the Horus Heresy – the bloodiest conflict humanity has ever known, civil war on a galactic scale, in which superhuman soldiers clad in advanced armour turn devastating weapons upon those they called brothers. Where do your loyalties lie?