Queen Yocasta was until recently, the very capable if autocratic ruler of Valermoore, but recently, she has changed. She is allways seen with a young woman, always wearing a heavy veil and gloves, who never speaks or moves. She claims that she is her daughter,Princess Chrysta, but a faint noxious smell comes from the veiled woman…
The local band of 'nasties' (goblins / orcs / whatever) lives in relative peace with the local population.
Along come the PCs and go through their usual heroic monster bashing routine, wiping out the nasties and pinching all their stuff, then continue on their way.
Problem is, they don't kill ALL he nasties. The survivors want revenge and, after spending a few months recovering, start to take it in their own inimitable style (which is not unlike that of the PCs come to think of it).
Next time the PCs are in the area they find themselves VERY unpopular with the townsfolk.