This book cleverly weaves details about life in the Roman Empire into a kid-friendly mystery.
Personally, I did not find the story all that interesting, but I will say that my 9 and 7 year-olds frequently asked me to keep reading when I intended to stop. Despite their interest, I think they were still too young to really keep track of the twists and turns in the story, and to figure out the implication of each.
There is also a fairly gruesome death at the end which, since it happens to the "bad guy," is, I presume, supposed to be a relief to the reader. While my kids were not terribly disturbed by it, I can't say I'm a fan of that kind of ending - at least not for kids this young.
Overall, it was a fairly painless way to learn about life in the Roman Empire, but the story itself... meh, I could take it or leave it.