From the Back of the Book:
In the province of Ling, Lord Yu has a problem: his mother. She's pompous and elitist and undercuts his actions by controlling the province guard. More recently, however, other problems started. Huge rats started appearing in alleyways. A six foot weasel was found in a hen house. Worst of all, an overpowering stench poured out from the drainage system. Lord Yu's guard, who have a touch of the lord's mother's ways, have been too "busy" to approach the task of finding out what is going on. Enter the adventurers, who, if they take the promises of cash and glory, walk into one of the truly messy situations of their careers.
The Jade Magi Sewer Crawl is a d20 system adventure suitable for fourth to sixth level characters.