I think that if I hadn't already read the Sub Rosa series by Steven Saylor, and the Colleen McCollough's series Masters of Rome, I would have enjoyed this book much more. A lot of the historical background is repeated and seems to take precedence over the plot.
However, if you have read neither of the above series, I highly recommend both this series and this author. In this particular book (the only one I've read of the series), you definitely learn a LOT about the Ptolemy rulers of Egypt, and about the great Hellenistic city of Alexandria! A nice change from the Ancient Egypt set in the time of the great Pharaohs such as Ramses, Akhnaten and Hatshepsut. It is also interesting to see the very biased viewpoint of the protagonist. As a staunch Roman, he has nothing good to say about Egypt! I found that a bit annoying; however, it makes his character more realistic.
Decius Caecilius Metellus the Younger is at it again - in the midst of trouble and trying to save the Roman Republic. I thought this mystery moved even better than the first 3 books in the series. The setting was Alexandria, in Egypt, and I really enjoyed the picture of this magnificent city that the author conjured up for me. Some of our favorite characters return - Asklepiodes is in Alexandria studying, Julia is escaping from uncomfortable circumstances in Rome, as is Fausta, but we are introduced to the enchanting 10 year-old Cleopatra, and a host of other fascinating characters. Can hardly wait to read SPQR V!