The Great Crusade reached its peak. The warriors of the Legion of the Thousand Sons were the most experienced in esoteric sciences, in the art of managing psychic energy, and in navigating the currents of the Great Ocean. Their home planet Prosperо was the center of sciences and arts. But no matter how loyal and devoted to the Imperium the warriors were, and even their primarch Magnus the Red, that did not free them from suspicions of dark sorcery.
And in the end, at the council in Nicaea, the Emperor forbade Magnus and his warriors—just as with the bibliarists of other Legions—to study the Warp and use the powers of psykers. When the unfortunate primarch foresees Horus’s betrayal and, in despair, tries to warn the Emperor by using forbidden powers, he puts his Legion in jeopardy—the Legion for whose salvation, long ago, he once accepted help from the forces of Chaos. And now it is time to pay back debts…