I have the opportunity for a little Deathwatch Campaign since my players where quite intrigued by my introduction mission: They were in search for a potential member of the secret organization 'Children of Achilus' just find out, that the officer was in search for a hidden Eldar placed in an ancient Word Bearer (pre Horus Heresy) outpost. After fighting back an upcoming Tyranid incursion, the players encountered a heavy attack craft of the Word Bearers entering the system and had quickly to decide what to do with the Eldar, held in stasis. They decided to destroy the outpost to not let the mysterious Eldar fall into the hands of the Word Bearers.
After that orbital bombardment, the players chose to quickly escape from the system and were called - I love cliches - by the Word Bearers: A Dark Apostel, with a Darl Eldar standing behind him, told the Marines that their action has been a dire mistake!
Now I am looking forward how to proceed.
At first, I need a Meta Plot for this mini campaign: What does a Dark Apostel of the Word Bearers want? My first guess would be something within the Omega Vault. But to reach this goal he has prepare his way into the Watch Fortress. At first, he has to find something within other pre Heresy outposts and second he has to find a way into the Watch Fortress.
I think it is very fitting to place further ancient outposts within the Cellebos Warzone, since the Stigmartus would be eager to follow such near divine beings as the Word Bearers.
But how to add a little more spice? What role does the Inquisition play? Is there an Inquisitor who is in search for the same device as the Dark Apostel? Is there a prophecy some Eldar are following? How about the Imperial forces? How do they react if a Kill Team comes and does not support any pleas for reinforcments? Or if the Kill Team spontanously helps the local troops, will the Word Bearers proceed without any hindrance?
I am open for any suggestions you veterans of the WH40k universe.