It was the legendary time. The Great Crusade carried the Imperial Truths into the darkest corners of the Galaxy, bringing scattered worlds of humanity back into the bosom of the Imperium and erasing alien races from the face of history. By the will of the blessed Emperor, who decided to step away from war, the reins of command for this unparalleled campaign were handed to Horus, the primarch of the Legion of the Luna Wolves.
So the chronicles say, but nowhere in them will you find the answer to this question—when, under the sky of which world, did the seeds of the Great Heresy take root? Perhaps it happened on the day Horus killed the Emperor for the first time…