Glistening in the light of Acheron, the crystalline structure of the Atrium is a fragment of Earth, carried across the void; a snapshot of green and blue amid the pale tans and reds of Tarterus, a promise and a dream.
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).