Magnus the Red, a mysterious occult lord, spent a long time studying the ancient art of warlocks. Now a psyker, rivaled only by the Emperor, commands his loyal legion of Thousand Sons in the Great Crusade, searching for lost knowledge along the way in the ruins of fallen human civilizations. Fighting alongside his brother, Perturabo of the Iron Warriors, Magnus senses an impending fork in fate - will Cyclops continue to fight in the name of common goals or will he direct his efforts to further knowledge of the warp?