Blood & Poison

"Rome. 26BC. Rufus Varro, spy of Rome, is ordered by Marcus Agrippa to help entrap a former drinking companion, one Publius Dio. But Dio, a ruthless smuggler and moneylender, is more connected and powerful than the spymaster imagined. Varro is drawn into Dio's web. If espionage is a game, then Dio is always seemingly one move ahead.
The agent is sent to hunt his enemy down, before Dio can arrange to murder Varro and his loved ones. Kill or be killed."