Okay, this is really more of a general sci-fi movie idea, but it could work in SSSS, and I want to get it down on figurative paper. I was inspired by the sci-fi miniseries Ascension on netflix, where the smartest people in the US are thrown in a ship on its way to Proxima Centauri to create a new civilization.
What if the rest of civilization haven't fallen? What if, the Rash and its effects on Scandinavia was just a controlled experiment? It's probably been done before, but I want to present a bit of a unique twist.
The experiment could start 6 months before Y0, with scandinavia being fed a bunch of false information regarding this mysterious new plague. Once this first step is completed to satisfactory fulfillment, step two commences: A biologically engineered plague, the Rash, is released in Denmark, and quickly spreads. But why? One possible explanation is that it was supposed to create a perfect society, where the nations band together for the greater good, or maybe to create superhuman abilities.
A possible story for this is that someone, like the cat-tank crew, discovers some kind of watchpoint close to the german border in denmark, and are faced with the leader of the experiment. In the spirit of conspiracies, let's call them "They" with a capital T