Murder! Not the most uncommon thing in the underdark, but this one the characters have been brought in to solve before it's even taken place. And several demonic cults seem to be involved! This is a mystery in the style of MURDLE by G. T. Karber (go check it out if you haven't!) meaning it's a puzzle which can be solved with nothing but old fashioned logical deduction. This one has a healthy serving of roleplaying opportunities and atmosphere on top. Written for level 6, but can easily be adjusted since the mystery itself is appropriate for any level. I especially recommend it for anyone trying to introduce a bunch of demon prince lore to their campaign in a fun way. Nothing helps players retain information like making it integral to an engaging logic puzzle.