Flavia, Jonathan, Nubia, and Lupus are on a quest for the Emperor Titus to steal a valuable gemstone known as Nero's Eye. The Delphic Oracle prophesied that whoever owns the gem will rule the Roman Empire, so Titus is determined to claim it for himself. Flavia and her friends travel across the Roman province of Mauretania, from Sabratha to Volubilis—or modern-day Libya to Morocco. As they travel on a caravan across the desert they encounter slave-traders, pantomime actors, and a wild animal stampede. Along the way, the young detectives must also try to determine what has happened to Uncle Gaius.