Lustrum, by Robert Harris.

Enjoyable and instructive read. Sequel to "Imperium".
For me, the most interesting aspect of the story is the account of Caesar's activities in the capital city up to the moment when he set out for Gaul. Caesar fascinates me. People decry the 'great man' approach to History: the idea that all that really mattered was what the major players did. They argue that larger forces, at work on a wider scale, determine the course of History, and that the great men were just the instruments of these forces. Greatness thrust upon them, in fact. But it is hard to maintain this position in relation to the changes wrought by Caesar.