Death Ex Machina (An Athenian Mystery)
Murder mystery set in Periclean Athens. This wasn't published as a young-adult novel, but--aside from a small amount of "adult content"--that's about its level. It's competently written, it has a moderate level of period detail, it doesn't go overboard in trying to convey the real alien-ness of ancient society, and the characterization is simple (one character, one adjective).
As a mystery, it's ordinary. If you don't spot the villain and the motive about fifty pages ahead of time, you're not paying attention.