Well, for my group, it's their Lord Inquisitor Flight, whom has been under the sway of Chaos for quite a while now. He's a closet radical. I re-did the Daemon from the Main Rule Book adventure (Name is slipping at the current moment) to my own specifications, and he currently has sway over him, and a large, deep Noble house named House Rowan. I could say they have two big bad guys, one being the Lord Inquisitor, the other being the lead of the radicalist house, Lionheart Rowan.
It's a bit tragic though. The group ended up getting some information that they did not realize what it was (it was saying that Flight was pretty much a dirty heretic) and did not read through it. They ended up passing the information along to their old Inquisitor, and Flight. Flight asked them who were the other's whom seen the information, and he ended up killing their ol' Inquisitor Austring, who was about to expose Flight, and thus, they are way set-back in the Campaign, with no idea of what's going on.
Although, I'm thinking of tying the Serrated Query to House Rowan somehow, and drop a few leads into the Lord Inquisitor's direction.
OH! That reminds me. Although, Flight and Lionheart are the two BIG baddies, there are 4 lesser baddies that continue to plague the Acolytes.
#1. Tech-Priest "Hammer". He is a Magos Errant whom has dwelled quite deep into Xeno technology. He's quite off the wall, and quite the fighter due to his augmentations (Has not been seen yet). He was pulled into Flight's group by Hammer simply seeking refuge, and word caught Flight's ear. Definitely the strongest, I'm keeping this guy 'till later.
#2. Sergeant Kane "Power" Nodd. This guy is a pyromaniac. He sets things on fire, and loves to just watch the flames dance. He hasn't been seen, but, he's been around, the group has never noticed a big 6'7" tall guy with promethium tanks on his back... Definitely the weakest, I'm trying to get this guy off'd in order to really continue the *Main* story, but, it does not seem to be working.
#3. Raven. This is the super marksman mercenary that Flight has hired. He's been in once, and that was just to take a super-long range shot at the guys, which ended up nearly removing the Psyker from the group (Whom ended up being a dirty heretic either way).
#4. The Mandrake. This Dark Eldar is "owned" by Flight, due to heretic technology being implanted in his head, basically making him controlled by the F man. He's also appeared once, to attempt to steal the Luminious Reproach and the Grimgoire of True Names. He almost got it, but, Agamorr had a few words. He's still alive, probably much to the surprise of these guys. The Mandrake is also quite the fast fellow.