Ever since the Imperium's rediscovery of the world of Chogoris, the White Scars' culture of warrior mysticism has sat uneasily with the ideals of Unity. As the Great Crusade burns across the stars, their enigmatic primarch Jaghatai Khan fights to preserve his Legion's distinctiveness amid a galaxy where cold rationality holds sway. Despite his self-imposed isolation, others in the brotherhood of primarchs seek to draw him into the greatest ideological battle of them all: the place of psychic power within the Legions. As the Librarius project is born, and opposition to it grows, the Khan must decide where his greatest allegiance lies - to the Imperial Truth, or to his own heritage.