BR 4 Oh Rats!! is a Fantasy Adventure Module designed for AD&D 1st or 2nd edition. I recommend 6-8 characters of levels 5-8.
This is the sequel to BR 1-3.
This adventure takes your players into a city of Vermin. These intelligent rats have found a source of power and their civilization is built upon it. Delve deep into the political struggles as sects fight and sabotage each others plans.
This 40 page module has everything you need to run as a standalone module, and has the framework in place to turn into a full mini-campaign. It includes the background, maps, descriptions and political system for a full city of evil Vermin.
Wanting to throw something different at your group, this module is made up of completely new monsters, new powers, new spells, new fighting tactics, new magic items, a new daemon, even a new artifact.
This module also includes rules on how to run a Vermin as a PC character if you wish.