The Otrevon Assault

From the introduction:

Situated at the base of a large mountain range, with easy access to a slow-moving river, lies the quiet town of Otrevon. Known primarily for it's exports of limestone from the mountain, it's the kind of town where excitement and danger are hard to come by. Until last month, when a large number of demons began to appear throughout the town. Many adventurers have flocked here to fight them back and make their names as heroes, but thus far no one has found a way to stop the relentless onslaught.