Fane of the Rat God

From the introduction: After waking up to a bristle of ratmen spears in their camp, the party is forced to go in the cavern lair of a large band of rodents. The being the ratmen worshiped ever since they moved in has been getting increasingly bloodthirsty and killing the ratmen sent to bring offerings. Being superstitious and cowardly, the ratmen "persuade" the party to take care of the problem, offering a reward if they succeed.