"Are we sane, we whose first instinct is to run to oppose the warp made actual? I ran to find a hallway of dismembered bodies, blood, warp–smoke, and a hazed but terrible presence already vanishing back to the warp at the far archway. I have listened to the vox record of Yand Mamin’s death many times, seeking to discern anything about nature of the daemon that slew him, a beast we now know as a Praedator."
–From the journals of Inquisitor Felroth Gelt: 3.056.789.M41
The Starry Order is a conspiracy of oblivion cults that spans the Ixianad Sector. Its heretics teach an apocalyptic creed---and for a century its fanatics have turned their eyes to Calixis and the Tyrant Star. Not content to merely preach, they seek to bring an apocalypse crashing down upon all. The worst of these cultists carry degenerate secrets into the Calixis voids, seeking greater sorcery with which to destroy worlds in Empyreal flames.
Upon a blasted xenos world in the 7th century M41, Starry Order archeoexplorators found what came to be known as the Conceit---a concept that is also a key to an ancient and potent pact made between an unknown xenos species and the warp. To know the Conceit is to become visible to the Praedatoris, malign ripples of the warp given form as implacable, invisible hunting beasts. These daemons search relentlessly and slay mercilessly, vanishing only when all who knew the Conceit are dead and torn.
Starry Order seers came to understand the cursed daemon-key, and it became a weapon in their arsenal of vile sorcery. The Conceit presently takes the form of a scroll of High Gothic script and some few diagrams, but it can also be explained verbally. Study or discussion of at least an hour is required to comprehend it, but that is usually longer than any would–be tutor has left to live. A psyker who knows the Conceit can project that understanding into other minds instantly, should his talents lie in that direction.
Once the Conceit is learned, a Praedator will soon come from the warp to slay and rend. The Praedatoris perceive the Materium through portals---any door, archway, or other method used by people to traverse an enclosing wall---and are constrained to materialize at a portal. A new victim of the Conceit is safe for so long as he goes nowhere near a portal of any sort, or remains forever enclosed like the vat–psyker slaves of the Starry Order.
A Praedator appears in the Materium as a series of twisting distortions of the air, with the barest suggestions of a hideous, flowing, amorphous form hidden beneath. Its invisible protuberances lunge and dismember with fearsome speed and strength. The daemon will not hesitate to slay anyone who comes within reach while it tracks the mind-scent of the Conceit. A Praedator is absolutely silent, even in the midst of tearing apart men and beasts that stand in its path. Very little can destroy it or turn it aside---and even then, another Praedator will emerge from the next portal the victim passes by. There is no escape whilst the Conceit remains known.
Very few manifestations of the Praedatoris have occurred within the Calixis Sector, though there is one known incident wherein Inquisitor Felroth Gelt encountered the work of the Starry Order upon Snowden's World.