So in the course of my Dark Heresy game, I love to thread various McGuffins into scenes; an Imperial Guard chaplain who may have shown some Pure Faith talents (nobody could see what happened, but the Daemon didn't kill the unarmed old dude before someone else stepped in to finish it), a Jokaero that lives in their base (filching bits and things and returning them all shiny and chrome), a Hellblade the Dark Obsession player locked in a vault instead of destroying, recurring individuals such as Leonard Jechinnarus the Hereticus Inquisitor (a great guy who advocated their euthanisation after exposure to a rather massive Warp incursion, three party members are still plotting ways to kill him because of that), Rogue Trader allies, nobles in the area, etc. I find it gives lots of flavor and later plot-hooks (the various trophies the party takes do this too; aforementioned Hellblade, Neural Agonizer, Gauss Flayer, Ork Power Axe, Kroot Rifle, a Splinter Rifle, all weapons that have nearly killed the party and ended up in their possession/trophy vaults).
They recently fought an incompetent cult. I built up a lot of suspense when they saw the rash of kidnappings and the two bodies they found had multiple Chaos symbols etched into them, of different Chaos Gods. They were jumping to 'oh no, it's Chaos Undivided, they're working together to kill us all!' In reality, the cult just barely had a clue about what they were doing. Half the party showed up at the final session due to scheduling problems, and the three less-combative PCs wiped the floor (I say less because while they aren't as good as the main ones, the tech-priest has an Omnissian Axe, the Psyker Primaris has a Force Hammer and the Astropath has a Power Fist. It was hilarious watching them flail and miss with these super-weapons and cause massive structural damage). What they find in the basement of the manor (hidden in a secret door in the fire-place with a sconce lever, utter cliche) is a dozen cultists who almost all get butchered (one immediately gave up when they heard someone say they needed to take only one of them alive), the prisoners and the cult paraphernalia. Such paraphernalia includes:
1. A full 'daemon skeleton' was the prize of the collection. Yes, Daemons don't leave skeletons, it was a fake with mold lines still on the bones. Still bad, because it was 'accurate' for a skeleton of something that has no bones.
2. Obscura-laced incense.
3. Ritual implements of dubious quality; the circle was actually crooked, and had it been used bad things could have happened to the people.
4. Some macabre items (human bits, athames that killed people, etc.). Some of them were of some cult-value.
5. Grimoires apparently written by kindergartners, judging by the quality. The runes and script were misshapen or spelled wrong (which translated to the symbols on the cultists too), Out of thirty books or so, only six had any accurate information in them.
6. A pile of other 'evil' things that were really just fakes and trash sold to the naive.
7. A dozen emaciated prisoners kept horribly. Their stories/identities match up and they're loaded up for debriefing/purity checks.
8. A single, better kept prisoner named Roger DeWitt, a local noble they'd grabbed a while back. His story checked out with an initial background check, so they kept him at hand.
9. In a different section of the manor, there was a phial/urn made of crystal and fire opal. Extremely pretty. It is filled with ashes, and the label at the base says 'Ashes of a Thousand Son.' Too much ashes to be from a single normal person, so obviously there could be a bunch in there. There was a notebook nearby, which explains the owner bought it and was quite aggravated as it was obviously a fake.
The party crates up everything that needs further investigation, the fine china and a carnodon skin rug, then proceeds fill the place with promethium, burn it down, then have a bull-dozer come through and level everything. Roger disappears during the drive home, leaving an apologetic note saying he's sorry for lying, he's not actually a DeWitt. He wishes them a good day, too. (I have three different plot-lines on what/who he could be, but that's another tale). The phial was kept by the pyromancer Psyker, as it is pretty and apparently not dangerous (she didn't Psyniscience it either). It currently sits on her mantle.
You all probably get the significance of Ashes of a Thousand Son. All but one player in my group (out of seven, two currently not playing) are actually unfamiliar with 40K as a whole; it's all new stuff to them and they learn the setting from in the game. The last one, my newest player, got bug-eyes when he heard what it said, but acted in character. None of them have Forbidden Lores related to Space Marines, Chaos Space Marines or the Long War/Horus Heresy. The database they have access to mostly covers Xenos stuff. They have no clue what it is, so they've put a couple lackeys onto trying to figure out what significance the name has.
Now, I haven't decided a few things so far; for one, should it be real? If no, bad things can still happen. If yes, there's more options. The second bit is they pinged Thousand Son in an Inquisitorial database. That might turn up somewhere and cause a ruckus. Or a traitor lets it get to hands who'd like to get their mitts on it. Who knows? Whether or not it is real, attention might be headed their way. Advice would be greatly appreciated, folks.