The Thieves of Ostia by Caroline Lawrence
Flavia Gemina is brilliant at finding things, so it's natural for her to solve mysteries. The daughter of a ship's captain living in Ostia, the port of Rome, in AD79, she acquires a gang of three friends who help her. There is Jonathan, the Jewish boy (and secretly a Christian) who has just moved in next door; Nubia, the African slave girl Flavia's father buys to save her from a terrible fate; and Lupus, a ragged homeless boy who is mysteriously mute. Together they work out who severed the heads of the watchdogs that guard people's homes, and why he did it. Caroline Lawrence, a first-time writer, is a terrific storyteller who creates a wonderfully vivid picture of daily life in the colourful, bustling port of Ostia while never labouring the historical detail. THE THIEVES OF OSTIA is first and foremost a whodunnit, with lots of excitement and plot twists.