Cthulhu Noir Help: A Yellow Night

[Tokuhara]

So I'm going to be playing a game with some friends of mine with a homespun system (CR vs d%, no ability scores/skills minus hidden Sanity tickers, based more on roleplay vs. rules) based in a 1940's/50's American Noir with H****r as the villain (keeping with the mythos, not saying his name aloud, as to not tempt fate) while keeping the Lovecraftian angle a secret from them. The idea is grisly disappearances in [Insert Witty Name for Chicago-Style Arkham analogue that doesn't tip my players off] that turn out to be from cultists of H****r, undoubtedly ending with them all either dying horribly or being driven mad by cosmic horror.

So here's where I need help:

1. I want to try and keep the Lovecraft side hidden from the party, leaving there no chance of metagaming. I want legit shock when H****r turns out to be involved, acting like a semi-generic gumshoe rpg with a homebrew system (mostly to allow for more freedom of action. CR for actions is based on my perception of character skill, so a Master Thief can pick locks easy, but performing an autopsy is not his forte) until Arkham Horror stuff starts happening, leaving the players as overwhelmed and surprised as the characters. How can I do this without making players VERY upset about the rug being yanked out from under their feet?

2. How do I tie H****r into a noir plot? To me, he's the most "usable" of the Lovecraftian Horrors and also not well-known enough to be an immediate guess. The idea is that people in the city are disappearing, leaving only a bloodstain on the ground, shaped in weird runes, so the Mayor grabs the sharpest minds including a detective (requested it to my players to insure one player plays a cop to make the beginning suspension of disbelief more acceptable) to figure out what's happening to these poor people, who are secretly being sacrificed to H****r to open a gateway for him to show up and do bad things to the world.

Thanks so much to anyone who helps me out!

~Toku~

[Yora]

If it's just a single adventure, I think you can simply change the theme to something unexpected and the players being fine with it. When the players expect the game to be just this one investigation with their PCs having no further use after it, it's much easier to just run with things, as you don't have any long term expectation.

The other question is of course, why do you want to use King Sunshine if you have no idea what to do with him?

[Tokuhara]

If it's just a single adventure, I think you can simply change the theme to something unexpected and the players being fine with it. When the players expect the game to be just this one investigation with their PCs having no further use after it, it's much easier to just run with things, as you don't have any long term expectation.

The other question is of course, why do you want to use King Sunshine if you have no idea what to do with him?

My plan is pretty much a two-part investigation where a simple string of disappearances turns out to have dire implications.

And to be honest, The King In Yellow is fear. In a noir setting, fear is power all its own. He is the fear of indescribable fear (saying his name alone has bad things tied to it), the phobias that have no rhyme or reason. And in noir, he's a terror in a setting that is already heavy with depression, dread, and hopelessness. There'll be subtle hints to him in the disappearances (the blood splatter shaped like the Yellow Sign, the only witness saying "I can't say his name...", gradual item drops becoming more and more occult, etc). My issue is I don't know what to do with him after the reveal.

[Tokuhara]

So... does anyone have ideas what to do with him after the reveal?