Border Kingdoms Fallen - Tier 1 Adventure 2
From the introduction:
Exiled to the remote marshes south of Derlusk, violent and traitorous radicals who call themselves the Consortium of the Crest are trying to cause mayhem and destruction in order to destabilize the region and restore the former kingdom. Taking refuge in their secret base of operations, Hollow Haven, the Crest is trying to bring fiends from the Nine Hells into the Border Kingdoms, and if they are not stopped, the fell will dominate the region and destroy everything in its path.
A four-hour adventure for 2nd-3rd level characters.