The Dead Cabal are a secret and select group within the Inquisition that is concerned with the events of the Dark Pattern occuring within the region of the Jericho Reach. They were created when the Deathwatch began the Long Watch, when only a handful of Inquisitors and Battle-Brothers were aware of the Pattern. As the lore was passed from one generation to the next, this Cabal was created to continue their study. This chain of events changed when the Achilus Crusade began that led to the rise in isolated incidents, wild reports and unfounded rumours concerning activity on the worlds involving the Dark Pattern. As a result, the Dead Cabal's scholars are watching these events and attempting to put the information together. Amongst their findings include the disappearance of twenty servitors at Vormos, a strange green glow amongst the skies of Castiel and the disappearance of an Explorator team on Sagacity.
In addition, they have noted the rise in activity amongst the Eldar within the Jericho Reach, which is unusual as this xenos species had previously been limited to raiding pirates or lone wanderers. However, now the Eldar are noted to be seeding the sector with their agents and taking an active involvement in developments. Those Inquisitors within the Dead Cabal have attempted to extract information from captured agents of the Eldar about their interest in the sector and their knowledge of the Pattern. This has, however, met with only stark horror with the fear these individuals experience being so great that they die before a Psyker can recover their senses. As a result, the Cabal believe that some ancient force predating man is stirring in the Jericho Reach that can prove to be more dangerous than both the Tau and Tyranids combined.