I need a little help deciding between the two ideas. The initial idea I started with was as follows:
The Weirdness: A block of flats has recently been plagued by a series of demonic apparitions of growing frequency and intensity.
The Problem: Influenced by extradimensional forces via a crack in the local rift, a young maths whizz is trying to perfect a reality-bending equation which will allow them to cross over into our world. The closer he gets to the solution, the more these entities are able to influence local reality, and if he succeeds in opening a portal to their world, the result will be no less than Hell on earth.
The Twist: Another group - a bunch of seeming religious fanatics with guns - are working to prevent this, and they have no qualms about killing the enthralled mathematician to do so.
The Enemy: Billy MacIntyre (the math genius), the Outsiders (his unnameable masters), and the Ordo Vigilia who are willing to kill Billy to stop him.
Possible Title: “The Doomsday Equation”
Combining that with the two Tales of Terror, I now have the following two ideas to choose between.
1) The Lloigor have possessed Billy and are using him to propagate the artificial intelligence algorithm detailed in version 2 of The Writing On The Wall. Reports reach the SOS team of mysterious 'mathematical graffitti' spreading in the city like a meme. As the algorithm spreads, people in the area (including one of the cast members) begin to experience nightmares and strange phenomena as the Lloigor begin to exert their influence once again. If not halted the algorithm will spread to such proportions that the Lloigor might be able to reassert their dominance over humanity.
2) Billy unintentionally constructed part of a mathematical formula for summoning Daoloth. In doing so, he attracted the being's attention, and it began to exert its influence over him. The summoning formula is too massive for Billy alone to implement, so on his master's instructions he leaves the mysterious writing on the wall in parts of the neighbourhood, which draws others under his power and allows him to work through them. As the formula grows closer to completion, locals begin to experience nightmares, reality is affected in strange ways, some people go insane. If not stopped, the formula will summon forth Daoloth, who will expand to consume the whole world.
So, which version do people like better?
EDIT: In a bit of further inspiration, I'm considering the possibility that Billy isn't actually a bad guy. Rather, because he's at the centre of things, the Ordo Vigilia think he's a conduit for Daoloth/the Lloigor, and their approach is rather 'shoot first and ask questions later'.