Way back when I was a member of Special Ops, I saw a fan-made demo adventure in the downloads section of the Special Ops website. It was about exploring a fallen covenant with a Criamon adulteration running loose.
Special Ops is defunct now, and I no longer have access to the website. Would anyone happen to have a copy of that adventure laying around?
Can you remember the name of the adventure? That would make tracking it down a bit easier. (Just from your description, it sounds a bit like an early edition of Val Negra but who knows how many fallen covenants with adulterations running loose are written about?)
I can't remember the name of it but it wasn't Val Negra. As I said before, it was fan-made, not an official Atlas publication, but it was part of the Special Ops set.
I only remember bits and pieces. The adventure had pre-generated characters, from 2 different Covenants, sent to explore a ruined covenant. The characters were thus forced into competition. I remember two magi and some Companions: a knight, an orphan-born thief, and an intelligent lynx. (I thought the pre-gen characters were brilliant, by the way.) There were some environmental obstacles on the way to the covenant. The covenant fell because there was a Criamon adulteration running around. I remember seeing themes that reminded me of Calebais, "Promises, Promises", and the Laboratory of Hermanus... don't remember a lot more than that.
I checked through the old UK Grand Tribunal wiki - the 2008 one has Neil Taylor storyguiding it, and Neil was very heavily involved in Special Ops so it's probably one he wrote.