 The novel details the first open move of the Heresy, the "Betrayal of Istvaan III", wherein factions of four Astartes Legions who were deemed unconvertible by their traitor brethren are ambushed during a planetary invasion of the fictional star system.The novel marks the first distinguishment of the "Loyalists" and "Traitor" factions within the Legions and other rebel forces, including the unmodified soldiers of the Imperial Army.4.