Rumours have spread to the ears of our adventurers, that mutants are appearing in growing numbers in a small village nearby. Reports of seeing mutilated bodies, strange monsters and dismembered corpses are drawing the players further into the intrigue. What's causing these events?
Maybe a crazy surgeon/sorcerer, who lost a son to mutation, is experimenting with taking apart and putting back together body parts, in order to find a cure to mutation? What is the moral outcome - should the surgeon be stopped, or will the players be interested in a cure too?
Maybe a necromancer is at work with warped and evil powers?
Maybe a piece of warpstone lays undiscovered nearby, and is turning the locals either mad or into mutants?
Maybe a deadly disease has broken out? Maybe the players catch it while investigating, and are forced to help find a cure or it would be the end of their days too...