Some men are born lucky, others are called Didius Falco.

It's the first century CE in Rome and informer and occasional imperial agent Marcus Didius Falco is miserable. The high-born woman he fell in love with, Helena Justina, has broken off their stormy, impossible affair. So when Emperor Vespasian assigns Falco a task that will take him out of Rome, he can't wait. Disguised as vacationer in the company of his comrade Petronius Longus, captain of the Aventine Watch, Falco travels south to Neapolis, Capreae and Pompeii where he discovers a conspiracy involving the Egyptian grain shipment to Rome. He also stumbles across Helena Justina, conveniently also on a trip out of town, who might, unwittingly, be enmeshed in this dangerous, treasonous scheme.
Lindsey Davis' Shadows in Bronze is historical mystery at its best.