The '''Dark Brotherhood''' were a group of [[Blackshields]] during the [[Horus Heresy]]. In 008.[[M31]] , after being cut off by the [[Ruinstorm]], they carved out a pirate empire at the edge of the [[Pale Stars]] and fought a long war against an [[Alpha Legion]] force tasked by [[Horus]] with crushing them due to their interference with his attempts to sway local planetary leaders to his cause.{{Fn|1b}}

In the bloody war that followed, both sides used hit-and-run and unconventional tactics. Eventually, a flotilla from [[Segmentum Solar]] under [[Council of Terra]] Lord [[Orpheus]] arrived seeking local support from against Horus' drive on the [[Sol System]]. Orpheus found a region in chaos, with the Alpha Legion, Blackshields, and other factions forming their own fiefdoms and spreading anarchy. Eventually the Alpha Legion's subversion tactics prevailed, forcing Imperial authorities from the system. Orpheus' messenger returned to Terra with the tale, and [[Malcador the Sigillite]] heard of the mysterious leader of the Brotherhood, [[Nemean]], and tasked [[Nathaniel Garro]] with bringing him into the [[Knights-Errant]].{{Fn|1a}}

As Garro negotiated with The Nemean, the Alpha Legion tracked him to the Dark Brotherhood's base and launched an attack. The Brotherhood then fractured in into mobs that fought each other, causing the disgusted Nemean to leave with Garro. In the aftermath of the ambush, the Dark Brotherhood carved their way across the region until they vanished into the Eridayn Cataract, not to be encountered again for an age.{{Fn|1a}}