A One-Round Living Greyhawk Duchy of Urnst Adventure
From the introduction:
The Rhenee are threatening all out war if the Duchy doesn’t meet their demands. Not that he is worried, but Ellis Lorinar suspects an unseen enemy is manipulating events. He needs allies he can trust for some covert investigating. But here’s the risk: it requires going so deeply undercover, you may never get back out.
This is an adventure for [character levels] 4 - 12, for versatile PCs who can handle highly unusual situations, far outside their usual comfort zones.