This is the fifth in Steven Saylor's "Roma Sub Rosa" series: murder mysteries set in classical Rome just before the fall of the Empire. Once again, Saylor's sleuth is Gordoianus the Finder, a sort of Sam Spade in a toga, who is hired by the rich and infamous of Roman society to solve their personal and political troubles. This time the powerful politician Publius Clodius is murdered on an open road and as riots break out, the fate of the Republic is in doubt. The plotting is deft and the action -- both physical and intellectual -- is nonstop. Most of the characters here are heterosexual but Saylor (who also writes great erotica under the name Aaron Travis) brings a critical gay sensibility to his tales that forms the cultural and emotional crux of his work.