The Sacrilege

Description for THE SACRILEGE by John Maddox Roberts:

"CAESAR'S WIFE MUST BE ABOVE SUSPICION!"

So decrees Caius Julius Caesar himself Rome's pontifex maximus, guardian of religious procedure. But scandal rocks the Imperial City when a sacred women's rite presided over by Caesar's spouse, Pompeia, is infiltrated by a corrupt patrician dressed in female garb. Decius Caecilius Metellus the Younger, fledgling senator and experienced detector of crime, senses a connection between the sacrilege and four bizarre murders that follow And with the aid of a notorious criminal, he will trail the bloody perpetrators from the lowest depths of the crime-ridden Subura district to the highest echelons of the Roman elite--creating powerful enemies along the way who are determined to terminate both the investigation... and the investigator.

This is #3 in An SPQR Mystery.