From the introduction:
They tell me the last guy to have seen a sunrise died last week. For as long as anyone else can remember, Necropolis has been shrouded in mists. You can wander the alleys or drive down the highways, but you always end up back downtown. No one knows when exactly the mists came or what they're made of. Some say it's an experiment in nanotech gone wrong, others say it's the souls of the dead, shredded by The Powers That Be like a legally damning document.
...
Necropolis is a cyber-gothic setting for The Sprawl. The player characters are cyberpunk professionals fighting corporations in a seemingly inescapable city which is possibly run by supernatural forces. To help establish this slight shift in focus, new moves for both the players and the MC are introduced as well as three new playbooks: The Sourcerer, The Necrotech, and The Mistwalker--for a bit of additional gothic weirdness.