Riven: The Horus Heresy Series (Unabridged‪)‬

As one of the vaunted Crusader Host, Brother Crius stood as the representative of the X Legion upon the soil of Holy Terra, but when he learns of the death of his beloved primarch Ferrus Manus at the hands of the traitors, his stoic, mechanical grief imbues him with the strength and resolve to undertake a special mission on behalf of Rogal Dorn himself.

Striking out into the stars, he searches for any signs of his lost Iron Hands brethren, hoping to bring them back to Terra to aid in the final defence of the Palace. The question remains - just who has survived the slaughter on Isstvan V, and what yet remains of them?