Who's Watching the Weir?

From publisher blurb: This is a short encounter set that is systemless and intended for 3rd(ish) level PCs in any OSR-style game. The design is deliberately vague in several areas to make it easy to "tweak & toss" into your current campaign. Perfect for when the party goes "left" when you expected them to go "right", any GM/DM/Judge can easily drop this into the current campaign.