A new Imperium is being forged across the galaxy. After millennia of isolation and localised conflict, the Emperor of Mankind has risen to rule holy Terra, and now commands his Space Marine Legions in reuniting all the lost colonies of humanity. At the forefront of his armies are the primarchs - post human warriors and leaders without equal, created from his own genetic template. This Great Crusade is all but over when Horus, the Emperor's first primarch son and Warmaster of the Legions, becomes part of a wider plot by the primordial forces of Chaos to corrupt mankind and bring fresh ruin to the galaxy. Swaying some of his brothers to his cause and facing others openly upon the field of battle, Horus has set his eye upon the Throne of Terra itself, and will not hesitate to let the Imperium devour itself in the bloodiest civil war in the history of mankind...