SPQR XII: Oracle of the Dead (The SPQR Roman Mysteries)

Decius Caecilius Metellus, this year's magistrate for cases involving foreigners, is living the good life in southern Italy, happy to be away from Rome, a city suffering war jitters over Caesar's impending actions. He thinks he is merely visiting one of the local sights when he takes a party to visit the Oracle of the Dead, a pre-Roman cult site located at the end of a tunnel dug beneath a temple of Apollo. He quickly learns that there is a bitter rivalry between the priests of Apollo and those of Hecate, who guard the oracle.
When the priests of Apollo are all killed, the countryside looks to explode in violence as Greeks, Romans and native Italians of several conquered nations bring out old enmities.  Decius is caught squarely in the middle, desperate to find a way out that will pacify the district and, incidentally, save his own skin.  This riveting series began with the Edgar Award-nominated SPQR and has gone on to international success in 13 languages.