This book is wild, beginning with elves kidnapping a young woman from 1968 Berkeley California and getting weirder from there. The elves and the Underearth combine Shaver's Deros with Robert Kirk's "Commonwealth of Fairies" (namechecked!) for a real tour-de-force of clammy horror and fairy tale structure. And then there's a nascent computerized fascist state in the last half for some reason, which works mostly because St. Clair's Underearth has jolted the reader out of their perceptual tunnel already. She also shows a real willingness to leave plot threads hanging and underexplain things, which might annoy some but for me remains part of the real frisson of fantasy and horror fiction, which this is.
If urban fantasy had followed Margaret St. Clair into the Berkeley Underearth rather than trailing after Emma Bull into the Minneapolis park system, I'd like it about three hundred percent more.