What is the main conflict in Roman Blood by Steven Saylor?

Marcus Tullius Cicero, a fledgling advocate in Rome, sends his slave Tiro to the home of Gordianus the Finder in chapter one of Steven Saylor's historical murder mystery Roman Blood. Cicero retains Gordianus to help solve a mystery. Cicero's client Sextus Roscius (filius) is accused of killing his father, a wealthy landowner. There are conflicting stories circulating about the reasons for the murder of Sextus Roscius (pater), and it is Gordianus's responsibility to untangle the details before the murder trial.