It was based in Greece or Egypt - I think Greece, most probably, at least that’s what the vibe was, from the foreign-sounding names
The civilization is decently advanced, as in, they have figured out sanitation and trading, and stuff like that
The plot revolved around uncovering the truth about a mysterious disease, most probably a certain type of plague
The protagonist is a teen, I don’t remember if he’s a slave or a peasant, or from a middle-class society. I’m not even sure if it’s a “he”, maybe it was a “she”? Or maybe I’m mixing the protagonist with another female character in the novel?
It is not a time-travel novel - no one from the modern time is involved
There was non-graphic mentions of murder, and something about conspiracy in the ancient society
There is also a slave side-character, who is a teen
The book had the vibe of Nancy Drew, Famous Five or the Secret Seven but in an ancient civilization
Maybe this could be the book. But the story isn’t exactly the same. I’ll try checking this one out.