"We just thought the winter was worse'n usual. Turns out we had an unexpected visitor. Wasn't until poor Dave and Glenda... died... that we finally got a clue. By then it was almost too late. You know how many of us'll never be the same? Oh, you doubt me, do you? Look in my eye, son, and tell me what you don't see. Yeah, I thought so. Damned Snow Devil!"
All you need to stop a brain is a bullet.
The PCs are sent with a diplomat to another country to protect him and do his bidding. There may be some espionage, rescuing, downright bullying, etc. Could make a nice medieval, special operations background.