Iacomus Artemidorus is an agent for the Caesars.
I put that 'employer' in plural because he sort of has multiple bosses though in truth, IMHO, just one. That one is Mark Antony who picks his targets and directs his actions, all on behalf of Antony's benefactor, Julius Caesar, and later Julius's proclaimed heir, Octavius. So Artemidorus works for Antony in service to the Caesars. Obviously this is all taking place in that tumultuous time of transition for the Roman Republic, the first adventure taking place in 44BC.
Note: in the famous play Julius Caesar by William Shakespeare, the character named Artemidorus is a minor player in the events but one with tremendously important information to pass on to Caesar in the form of a letter, one that Caesar will to his regret never read. In that epistle, Artemidorus lays out the principal plotters in the assassination. A different take on this interesting fellow is presented here by author Peter Tonkin wherein Artemidorus is not a seer of the future but an intelligence agent who has scoped out the conspiracy and its members and who will strive to alert the military leader to help stop the attempt.
The Artemidorus we will follow is a Greek by birth [Spartan, to be more exact] who would train as a soldier and become a centurion in the VIIth Legion. He would also come to the attention of Mark Antony who recognized talents of many sorts in the man and who would put him to different uses than just skill with the gladius sword.
These adventures will take him - and, luckily us alongside - through those very dark Ides, passed the killing of Caesar, and into the beginning of the Second Roman Civil War, times which will really demand a secret agent, as he is referred to often as, with the skill and tenacity of Artemidorus.