A new story is frequently being whispered in the dark corners of taverns across the country, telling of a traveler that occasionally appears in quiet, rural towns; that draws with him a plague worse than any other: a dragon's wrath.
The player characters, experienced and somewhat well known, hear rumors and travelers' tales about a distant area being overrun by dragons (or other terrifying monstrosities). The locals have sent them a message, begging for heroic aid.
When they investigate, they discover that nothing of the sort is going on. It turns out that a group of thieves wanted them out of the way so that they could rob them (or someone who would normally receive their protection).