“The great hulk of the scaled beast lay wheezing before me, and I am not ashamed to say that I was frightened: though it was injured, I knew the dragon could easily tear me in twain. The young monk, however, knelt beside the creature’s head, whispering to it in a strange growling tongue. I questioned the woman, but she ignored me completely, engrossed in examining the scaly monster. After much badgering, she said merely, ‘I do not mean to be rude, but you are quite a distraction. Please, leave me to my work.’” -Jeron’s Great Journeys, Book III, Chapter 4
A plague has hit the local area.
In humans it affects only the most vulnerable, the children and the very old, and even than it's little more than a summer cold. 24 hours of sniffles and then it's gone, barely noticeable really.
To sheep however it is fatal and the whole economy of the area is in serious trouble. If this keeps up the area could well be facing famine.
Somebody (enter the PCs) must find the rare herbs needed to make a cure.