Shadows In Bronze by Lindsey Davis
Rome. AD 71. Marcus Didius Falco, now Imperial Agent to Emperor Vespasian, has not been resting on his laurels. Tidying up corpses, kicking over the traces of a failed coup, making a bit on the side in stolen lead ingots - it's all in a day's work for an ex-private eye. But a new plot to usurp the purple robes of power puts Falco on the back of a mule with a one-way ticket down the Appian Way - bumping into trouble, treason and Helena Justina, a senator's daugher he's trying hard to forget.