The PCs are troubleshooters who work for an aasimar named Serendipity (a former Paladin of Dol Dorn) and have been hired to head to a backwater locale in the Astral Plane.
They're tasked with finding a rogue modron named Twonky whose residing on the decapitated head of the dead god, Khnum. Khnum's corpse was destroyed decades ago in a skirmish between the Githyanki and the mysterious Throng.
Serendipity has a source waiting for them at the Looted Corpse, a tavern in outpost known as Krull.
Serendipity wants Twonky because she believes he can lead her to the Rod of Seven Parts...and a benefactor who can resurrect her family.
When looking at DnD there are quite a few locales to narrow down. This idea let's me stir it all up and run with it, plus it lets me try the engine out at around 9th level. Its in the lead at the moment, especially after finding my Planescape Boxed Set from ADnD 2E.