This is one of my better adventures, the problem is that I didn't GM it correctly so the players didn't get scared. :-( Tip: Read "The Shadow over Innmouth" (sp?) by Lovecraft first.
On a medium big island (4-6 miles across) there is a village and a mansion a mile or two from the village. A forest lies around the mansion, which is next to the sea. The mansion is own by an eccentrically man who only has one servant. He also have a brother in some big city (who's a doctor).
One day when one of the people in the village comes up to the mansion for some purpose he discovers that the front door is partly open. In one room he finds all the furniture put away up against the walls and a lot of signs is carved in (with a knife or similar) into the floor, walls and roof. On the middle of a big symbol there is a body, recognised as the brother of the master of the mansion dead, sacrificed. The servant and mansion owner are no-where to be seen. The villager sends for help.
Tahadaah... The players enter the scene from the left... :)
During the search in the house they goes into the kitchen and then out of it (nothing interesting there, they shouldn't be allowed to investigate too much here...). After a couple of minutes they find that they are missing one of the NPCs (anyone you like) who was following them. They finds him in the kitchen, killed with a meataxe with tremendous force. They haven't heard anything! They should realise that someone (something?) was in the kitchen WHEN THEY WHERE THERE TOO! Dahdahdaahda!
It's the servant (who is 800% insane and lives in the forest on the island) who killed him, when returning to steal some food.
Handouts:
A letters from the mansion owner's brother. They are talking about what a grandfather did to his daughter (married her to a Deep One, but that's not said straight out) and in that way "put this curse on our family". He also talks about fact that he has found a medication against this ("my eyes are once again normal and I don't have to wear sun goggles in the middle of the winter"). He also says that he "comes home to cure you my dear brother, even though it seems that you don't realised what a curse this is". The last letter says that the brother arrives the night before the man from the village finds his body and ends with "Stay out of the water, for God's sake!". You may also give them a unfinished letter from the Mansion owner saying he is rejecting the offer. He thinks the grandfather did the right thing.
What has happened:
Persons involved: The Mansion owner, who is Deep Ones (or "Deep-Ones-will- be"); his doctor brother (who doesn't want to be one); the mansion owner's servant.
The mansion owner thinks the Deep Ones connection is the best thing that has ever has happened to him (there are letters telling about this in the doctor brother's home and they both write diaries). When the doctor-brother arrives late at night his brother is prepared. With the help of his servant (they both completely insane) he strikes down the doctor and sacrifices him to some Outer God. The servant now extremely insane (SAN= -[VERY big number] ;-) ) runs away out into the woods (it is he who kills the NPC in the kitchen when he tries to collect some food. He will later try to escape to the mainland and run to some place, not even himself knowing where to (maybe a secret temple, but that's another story)). The mansion owner escapes down a tunnel to the ocean, down to a Deep One-City.