From publisher blurb:
Rust Monster Mine is a Fifth Edition plug-in adventure for four characters with an average party level (APL) of 3, 5, 8, or 11. This document offers a general guideline on how to scale the adventure for each level. A newly excavated mine has attracted a number of rust monsters who’ve begun to feast on its riches. The characters must enter the mine and save all that sweet, sweet metal—they may even come out of it with a small business!
The Rustmine is a series of caves and tunnels that would be unremarkable if it weren’t for their rich veins of iron. It was built by a Dwarven mining company led by Thidrubelle Birdwatcher, head of a merchant clan of small means and large ambitions. Unfortunately for them, their big break soon turned into a deadly nightmare. As the dwarves dug further and further into the earth, they began to attract hideous monstrosities that seemed to feed on the mine’s raw ore. No one has heard from Thidrubelle in some time, and inquiries have been made to see what’s become of the company—and their mining rights.