I am a huge fan of the Roman Mysteries series, both in book form and TV adaption. These books take something of the concept of the Famous Five (four child detectives and a dog, tracking down criminals and solving mysteries) and sets it in the ancient Roman empire. This is a gritty and realistic ancient empire though, and as such it is highly educational, very exciting and a really good read.
In this book the children are far from home, travelling the ancient Roman province of asia minor, in pursuit of a slave dealer.
The story is first class, and brings together some threads of earlier novels.