Under Illefarn (Advanced Dungeons and Dragons/Forgotten Realms Module N5)

Daggerford is fairly quiet for a frontier town. Sure, lizard men raid the local baron's holding now and then, orcs sneak out of the Misty Forest to raid caravans on the Trade Way, and lady Bronwyn has a few suitors who are a touch too passionate, but there's nothing going on that a member of the renowned Daggerford militia can't handle.
Except that the Shining River has turned green, the cattle are dying. Except that the Elf King of Laughing Hollow, a place where no human dares to go without fearing for his life, is asking the militia for help. Except that strange substances are oozing from the fissures caused by a recent earthquake. Except that the earthquake also has opened an entrance in the cliffs around Laughing Hollow that might lead to the fabled dwarf mines of Illefarn.
Suddenly, being a militiaman isn't quite as easy as it used to be...