A baron or ruler of a territory beset by some type of disease or malady (could be of the biological or magical kind really.) has lost contact with one of his / her villages. They've hired the adventurers to go and check out why.
Turns out that the village is actually safe from whatever is plaguing the rest of the area. The reason of course is that the villagers have turned to demonism and are being blindly led (or maybe not so blindly?) by a necromancer. The mission is to get rid of this menace, whether it be the necromancer alone, or the village as a whole.
Although, I must admit, a bit of subterfuge is a wonderful thing. Some drugs / potions to falsely lead characters into believing something that isn't so... whatever. But there is a lot of room for head games here. NPC interactions could be a large part, and in fact should be, of solving who or what is behind this.
Sure, there are a couple of modules that are fairly similar, Danger at Dunwater, Temple of Set, etc. but overall, I think that after watching this movie, you'll agree, it's a really cool setup for a neat adventure.