I enjoyed this book for the most part, but am uneasy about it.
The story is interesting and not as predictable as many books I've read, although the children's intelligence level does seem to fluctuate a bit depending on the needs of the plot.
However, I almost gave up on this one on the first page. The first characters we meet are an Arabic gent named Hussein Hussaout and his son Baksheesh and dog Effendi. "Baksheesh" means something like "alms" or even "bribe" in some places and "effendi" is a title for a learned person. So the author's use of them as names seems to be potentially quite offensive or at the very least lazy research. I decided to press on only to find that later we encounter characters called Toeragh and Huamai. I get the impression that the author thinks he's being clever and witty, rather than deliberately mocking the Egyptian characters, but that doesn't mean he won't have hurt people's feelings. In fairness, it isn't only the Egyptians who receive this treatment - there's a French character named Mrs Coeur de Lapin (rabbit heart - presumably a reference to the unfair stereotype of the French as lacking in courage) and Nimrod's English servant is named Groanin - but it seems more obvious with them.
At one point in the book, Philippa says something about the need to show more respect for other cultures. If Kerr had taken her advice I might be able to recommend this book with a clear conscience.