The Venus throw - Steven Saylor

On a cold January evening in 50BC, two strangers enter Rome - one an Egyptian ambassador and the other a eunuch priest.
Both are seeking Gordianus the Finder, who has a reputation for solving murders.
But the ambassador, a philosopher named Dio, asks for something Gordianus cannot give - help in staying alive.
And before the night is out, Dio is brutally assassinated.

Now Gordianus must begin the most dangerous case of his career. Hired to investigate Dio's murder by a beautiful woman with a scandalous reputation, he will follow a trail of intrigue into the highest circles of political power and the city's secret arenas of debauchery. There Gordianus will learn that nothing is as it seems, not the damning evidence he uncovers, nor the suspect he sends to trial, not even the real truth behind Dio's death which also lies shrouded in secrets - though not of the state, but of the heart.