Caius Julius Caesar, now dictator of Rome, has decided to revise the Roman calendar, which has become out of sync with the seasons. As if this weren't already an unpopular move, Caesar has brought in astronomers and astrologers from abroad, including Egyptians, Greeks, Indians, and Persians. Decius is appointed to oversee this project, which he knows rankles the Roman public: "To be told by a pack of Chaldeans and Egyptians how to conduct their duties towards the gods was intolerable."

Not long after the new calendar project begins, two of the foreigners are murdered. Decius begins his investigations, and, as the body count increases, it seems that an Indian fortune-teller popular with patrician Roman ladies is also involved. Decius figures out the fortune-teller's scam and also exposes the foreign astrologer who carried out these murders—almost losing his life in the process.

This latest in the acclaimed series is sure to please historical mystery fans.