From the introduction:
Apeiron – the ghost world – is a lot like ours, except that the decaying remains of the past are everywhere. Boats left to rust and decay on deserts that were once seas or lakes. Buildings crumbling and ruined. Cars left to rust on the side of grass-broken roads.
Everything silent and still and dusty and full of that oppressive feeling that makes your hindbrain gibber in panic and demand you flee, only there's nowhere to flee to.
Nobody knows why some people end up here, instead of wherever they're supposed to go. Some folks, most folks, band together in communities, building walls and eking out what meager living they can, fearful always of what might come next and what's outside the walls.
Fate Eidolons, marshals and drifters, of a sort, have the job of keeping the peace, settling disputes, and, if you get to know one well enough, looking for a way out.