Everglade

From publisher blurb:

Marquis Anton Aumarais is planning to throw a grand ball, but needs servants (the PCs) to replace those who’ve been rendered unavailable. It’s not long, however, before a night of fun, food, and camaraderie becomes a nightmare of misery, pain, and death. The problem stems from the swamps that adjoin the Marquis’ property, and the PCs are asked to help deal with it. But the swamp hides not only a reclusive backwoods people but a dire secret that might be too much even for the vaunted heroes to overcome.

Everglade is a short adventure for 2D6 science fiction RPGs such as Cepheus Engine and the Original Science Fiction Roleplaying Game (OSFRPG.)