 It is planned and led by the Traitor Word Bearers Legion, now fully and openly committed to the spread of the Primordial Truth.The narrative starts close to where the timelines of Book 8 and Book 14 converge (in their respective conclusions), with the invasion force en route to, or near the planet.The rebel mission has aims beyond just delivering a crippling blow to the Ultramarines Legion and their home system; its objectives may affect the entire Heresy campaign.