Imperium is the first in a trilogy of novels about the life and times of Marcus Tullius Cicero, one of Republican Rome's most famous orators and politicians. The book is narrated by Tiro, Cicero's slave and secretary, many years after Cicero's death. Tiro existed and is thought to have lived to be a hundred years old. He was famous for creating a short hand that he used for taking notes and later was adopted by the Senate. There is considerable evidence he wrote a biography of his former master, but those books are lost to history. Harris gives him back his voice. 
 The story is primarily a political thriller--there is little physical action and only a scene or two in which there might be some physical danger. Tiro is a wonderful, sympathetic character--intelligent, loyal, hard-working; brave when he needs to be; and, at all times, discreet. His "voice," through Harris, is straightforward narrative with not a lot of reflection or poetry, but excellent descriptions of places and people--what you might expect from a person who spends his life listening, watching and recording. 
 As to the plot, if you don't have some familiarity with the players and events of the times, it can become a bit confusing. The action takes place between civil wars and dictatorships with a young Julius Caesar just starting to play a role in politics. Harris does a good job of weaving the historical details into the narrative without boring the reader, but it still helps to have some background. There are plots within plots, shifting factions and loyalties, and the minutia of governing. 
 Harris does us a favor bringing this famous Roman back to public notice in such an accessible story. Since Latin is no longer required in high school or college, Cicero is fading from our collective memory. Which is a shame--he profoundly affected our U.S. founding fathers. Because so many of his books and letters survived, his work became canon in studying the language and his views on a balanced government suffused the ideas of Enlightenment thinkers and are reflected in our constitution. John Adams' first and most prized book was his Cicero. I recommend Imperium and will be looking forward to the next installment: Conspirata. 
 I've posted a more extensive review at my blog.