Last Sunday I threw the hook for a new story arc in my DH campaign. The basics of the setting are as follows:
An ancient and powerful alien device (weapon?) was recently "activated" for a short period of time within the Jericho Reach, resulting in an apocryphal discovery within the Omega Vault of Watch Fortress Erioch. The "End Times" are nigh. Mankind stands on the brink of...well, not annihilation or extinction, let's just say the Imperium will be drastically altered. In order to preserve Mankind's true manifest destiny, a tiny cabal of Inquisitors, Rogue Traders, a Deathwatch Captain and a Calixian Fleet Commodore have gathered together a flotilla (including a Universe-class Mass Conveyor) and populated it with Imperial citizens from all tiers of society, all walks of life, many Imperial worlds. Aside from a rare few (relatively speaking) no one knows the hive they live within is actually a space-faring vessel. Instead, they believe they are colonists, brought to live upon a planet whose atmosphere outside of the hive structure is inimical to human survival. Borrowing a popular movie title, I have named the "hive" AXIOM.
In relative terms, the screening process was somewhat of a rush job. Accordingly, there exists a distinct possibility that all sorts of ne'er-do-wells are hidden away in the dark places under deck plating and between bulkheads, and/or within the aristocracy, crew, and command elite. Entire cities, relatively small hives themselves, span each of the inner decks of AXIOM, and travel (which is extremely rare) between AXIOM "Prime" and the lesser "hives" is blinded. The ruling elite are nothing of the sort, the true masters of AXIOM being the flotilla's Commodore and the Captains of smaller attendant vessels. The Inquisition's power and authority, while repected, is hobbled by the greater, long-term consequences of AXIOM's fate. Aside from dangers conjured by the mind's wildest imaginings, there are also mundane issues such as overpopulation, limited resources, low morale, etc.
I invite those of you so interested to read the two-part space opera 'The Risen Empire' and 'The Killing of Worlds' by Scott Westerfeld, and imagine what it would be like if, in the twilight days of the Imperium, the Emperor awoke, stepped down from His tenthousand-year imprisonment upon the Golden Throne...and was not pleased, even in the least, with what He saw. Imagine the Adeptus Mechanicus rising to become the "new ministry", known as the Imperial Apparatus, the Emperor Himself denouncing His own divinity, and the Imperial Creed prosecuted on a galactic scale. Imagine Terra in ruins, the birthpalce of Man nothing more than scattered debris floating in space...
While the greater Imperium beyond the boundaries of the flotilla are caught unaware by the changes yet to come, the Acolytes (with the occasional cameo role filled by Space Marines of the Deathwatch) must protect the last bastion of Humanity...no matter the cost.