Blood Debts — Ashley Gardner

Leonidas, freedman, once the most popular gladiator in Rome and champion of the games, now must fight for his life outside the arena. A man who owed him money was murdered, and Leonidas is a prime suspect. With the assistance of Cassia, daughter of a Greek scribe who was bestowed upon him as his slave, Leonidas fights for justice in the back lanes of Imperial Rome.

Cassia has no idea how to cook and clean or mend and weave, but she is very good at finding things out and writing things down, able to work through a dozen mathematical problems by the time most people can think of a sentence. Knowing both intuitively and empirically that Leonidas is innocent of the murder, she resolves to help clear him of the crime. It's the least she can do for a man who has proved to be far less brutal than his reputation and who protects all who come within his sphere. And if Leonidas loses, he faces a short, painful future back in the amphitheater, this time without hope of survival.