Karneval is SFF with mystery elements. I'm pretty sure I bought my copy new but steeply discounted, as part of the closure of my town's only new bookstore.
Review:
This starts with a child-like teen (young man?) named Nai being handed over to Lady Mine, possibly for sex but more likely for food (or, you know, both). They're interrupted by the arrival of a small band of thieves. The leader of the group, Gareki, sees Nai's bracelet and recognizes it as something valuable - it's the ID used by Circus, a special group devoted to hunting Varuga. He helps Nai escape in the hope of getting his bracelet and selling it. Nai, meanwhile, would happily give it to him but wants to ask permission from its owner first, someone named Karoku. Karoku is an important person to Nai, and he badly wants to find him again.
Gareki figures that Karoku must be a member of Circus, so he focuses on getting Nai to them. Unfortunately, Nai is a bit stupid and requires constant supervision. When they do eventually get in touch with Circus, there's no Karoku, but a little investigation results in some shocking revelations about Nai's identity.
