The Great Crusade had reached its apogee. The warriors of the Thousand Sons Legion were the most sophisticated in the esoteric sciences, the art of controlling psychic energy and navigating the currents of the Great Ocean. Their home planet Prospero was a center of science and art. But no matter how loyal and devoted the warriors of the Legion and their primarch Magnus the Red were to the Imperium, this did not rid them of suspicions of dark witchcraft. And in the end, at a council in Nicaea, the Emperor forbade Magnus and his warriors, as well as the librarians of other Legions, from research the warp and the use of psyker powers. When the ill-fated primarch foresees the betrayal of Horus and in desperation tries to warn the Emperor using forbidden powers, he puts his Legion at risk, for the sake of whose salvation he once upon a time accepted the help of the forces of Chaos. And it's time to pay debts...