Phalanx, the great star fort of the Imperial Fists, is playing host to Space Marines from half a dozen Chapters, alongside Inquisitors, Sisters of Battle and agents of the Adeptus Mechanicus. They have come together to witness the end of a Space Marine Chapter, as the once-noble Soul Drinkers, now Chaos-tainted renegades and heretics, are put on trial for their crimes against the Imperium. But dark forces are stirring and even this gathering of might may not be enough to guard against the evil that is about to be unleashed...