I just watched the movie God Told Me To the other day. It's a 'grindhouse' staple from 1976 that I have heard about for, well, decades, but never got around to seeing. Turns out, it's not very good, but it occurs to me that the basic plot would make for a great Dark Heresy mission with only a little tweaking:
---SPOILER ALERT (I dunno, do you still need to do that when a movie is nearly 40 years old?)---
A series of spree killings are plaguing the city. The perpetraitors usually commit suicide; those that are taken alive are surprisingly docile. When asked why they went on a killing spree, they smile and say "God told me to…" Investigation reveals that the killers have one connection: they have all crossed paths with a bizarre messiah-figure. He is fairly easy to identify; his records indicate that he was supposedly the product of a virgin birth. When the investigator tries to locate this individual, he draws the attention of a cabal of powerful men (politicians and business leaders) who are under the influence of the 'messiah', who has actual 'miraculous' powers (including psychically compelling the killing sprees) and whom they whole-heartedly believe to the the Second Coming. The truth, however, is that the messiah is actually a human/alien hybrid, implanted into a UFO abductee… It's mostly downhill from there, as the film relies on an absurd contrivance to come to an unsatisfying conclusion (-that never adresses why the hybrid(s) were created in the first place).
A little tinkering can turn this into a good DH scenario. Obviously, the hybrid should be suspected of being a new Living Saint. Maybe the Acolytes are dispatched to investigate that possibility, and subsequently learn about the mass killings- and investigate the possibility that they are connected. Rather than have the hybrid be the 'ultimate' adversary, I would have him be a pawn of his alien 'daddy': maybe he truely believes he is a Saint and the voices he hears in his head are from the Emperor, 'calling the faithful to join him' (that provides a good excuse for not having to make Decieve rolls when the PCs meet him). For the alien progenator, I would make his motivation that his warp vessel is damaged; it is hidden in a deep crater on the planet's moon (perhaps lying there for thousands or millions of years), and it needs psychic energy to power up. Toward that end, the alien has used the last of his ship's power to create a powerful psyker hybrid that can influence the population to mass murder (the killing sprees always occur when the moon is directly overhead); his vessel then absorbs the psychic energy released by masses of violent deaths- in effect the ship is powered by stolen souls. What will happen if/when the vessel reaches full power…?
Using big-budget movies as the insperation for rpg scenarios usually results in groans from players as they immediately realize what's going on, but less-well-known B-movies have potential for inspiring some good scenarios- and even if one of your players picks up on the source for the plot, they are more likely to respond with a sly nod than anything else…
So, anyone want to suggest other B-movies that can be given the Grimdark treatment…?