The Awful Truth
Though there’s a lot of talk about ghostly canal boats, much of it is being pushed by a cabal within the Ousatonic stockholders. They’re hoping to cloud the debate, and snap up as many shares as they can before the price gets pushed up. The cabal sees the disappearance of the surveyor as a godsend; the more people get caught up in the hoodoo angle, the less likely they are to pay attention to the share price.
However there is a Mythos angle. A larval Colour was brought to the
four months prior, and has been growing there ever since. While it is nowhere near strong enough to leave, it has power sufficient to deal with wandering surveyors, and possibly also the protagonists. Red Rock Canal
I like the Colour out of Space; it's a breathtaking, atmospheric short story. However as an RPG antagonist it has its flaws. It doesn't travel. If the protagonists are to encounter it, they have to go to its location. It doesn't have much of a written history; no mention in those worm-eaten grimoires, and even if there were, they wouldn't point to its current location, only to where it had previously been. So I can't drop too many clues, as there wouldn't be many to begin with. I suppose I could generate a few newspaper articles and bombard the players with them right at the start. A lot of the old Call of Cthulhu scenarios started that way, but it seems contrived. The protagonists won't have a reason for doing anything, other than The Plot Says This Way, Therefore This Way We Shall Go.
So if I want the protagonists to face a Colour, it probably has to be a completely accidental encounter. They were looking for something else, and found It. The encounter probably also has to take place in a remote location, since otherwise there'd be plenty of other people trying to investigate. I suppose you could make a story out of that - say, make the Colour the centerpiece of a circus freak show - but it doesn't seem to fit with the short story's concept.
So here I have a remote location, the wilds of New England and an abandoned canal with a mysterious past. I lure the protagonists in with the prospect of riches - someone's trying to cheat them out of their Ousatonic profits! A bit Cat and Canary I admit, but it works, and it gives the protagonists a very personal reason to penetrate to the heart of the mystery.
One thing I've noticed about players: as a rule, they tend to think that if they've encountered the plot, they've 'solved the mystery.' They don't look beneath the surface, preferring instead to take most things at face value. So I can drop a few Colour hints without worrying too much that this will give them pause. Odds are, they'll trot obligingly into the lion's den - and then the fun begins!