I'm currently reading Death and a Crocodile by Lisa E. Betz. I believe it's a stand alone, but may be the start of a series.
Life is difficult in Ancient Rome, even for respectable young women such as Livia Aemilia. Her father has decided she must marry an aristocrat instead of the handsome family friend she admires. When her brother breaks the news that their father has been murdered, the two soon realize that this was not a robbery gone bad, but murder. Their scheming uncle accuses Curio of patricide and Livia knows she must search for the real killer. If she doesn't succeed she may not only lose her brother, but be married off to someone worse than an inscrutable senator. With her plucky slave and her new faith Livia will search for answers. But will she be stopped before she can reveal the truth?