Aha! So you're a fantasy author, are you, Mr. Watt-Evans?
I think not. Not exclusively, anyway. This is damned good work.
"Nightside City" works both as SF and as a detective procedural. The plot is more than adequately complex, the mystery a fair challenge, and the setting against which it plays out, a resort city on an almost-but-not-quite-tidelocked world that will soon become uninhabitable, is both original and evocative. The only comparison I can make is a somewhat distant one: the "festival planet" Worlorn in George R. R. Martin's "Dying Of The Light."
Carlisle is well characterized, both tough enough and simpatico enough to get the reader attached to her and keep him that way. Antagonists Sayuri, Paulie, and the rest, even though we don't see much of them until well into the book, work just fine. (I particularly liked that Sayuri is as utterly consumed by wishful thinking as she is.) The Supporting Cast characters are adequate to their roles, though not more, but that's to be expected in a tale of this kind.
With regard to style, the opening of the book did give the elaborate feeling of something out of high fantasy. I was pleased to see you tamp it down before it could interfere with the meat of the tale. Overwriting is a death sentence for a police or detective procedural -- and it doesn't take much to be considered overwriting in those genres.
If I had to guess at the story's theme, it would be the power of wishful thinking. God knows, it has muscles, and Sayuri, the spoiled rich girl determined to prove to her plutocrat relatives that she can cut the ice just as well as they, was a near-perfect vehicle for dramatizing that. The ironies involved in the denouement, as Carlisle "turns Sayuri in" to her elders on Epimetheus, were also quite satisfying.
I look forward to reading "Realms Of Light" and, should the Spirit ever move you to complete it, "The End Of The Night." Well done.
(reviewed the day of purchase)