I'm not sure to what level of plotting and subversion is portrayed in the book but I'll try and explain what is known to modern day historians in a condensed format. (I'm guessing if Cicero is the main protagonist then Ill assume Caesar is the antagonist and may be cast in a more negative light) Also quick side note, technically he wasn't emperor, he was dictator, a magistrate of the Republic with full authority over the state during a time of crisis, military emergency etc.

Caesar is known to have bribed and manipulated his way to power just as dictators such as Sulla did decades before. But bribery and intimidation was something common amongst the senators of the Roman Republic. He made deals with prominent senators and people of interest. He was part of political group that is known as the first triumvirate, with Caesar, Pompey and Crassus, two of Rome's most powerful and richest men. They dominanted the political scene for awhile, pushing laws and edicts that benefited them. This was how Caesar managed to gain governorship of three provinces which led to his conquest of Gaul. He married family members to other powerful senators to gain connections and patrons.

He used various ways at his disposal to gain infamy, money and power. His conquest of Gaul for instance was to gain military prestige and cash from the sale of subjugated natives. The way he justified the war was framed in such a way as to appear that he was protecting Roman allies and interests in the region. His foray into Britain was pretty much a publicity stunt, as no Roman general had stepped foot on the mysterious land. He bent the rules and even just blatantly ignored them when he could and probably had a hand in back room dealing and subversion and downfalls of his political rivals.

Overall, Caesar did many things to obtain the reigns of power over the Roman Republic, though he didn't do anything no other senator was doing or had done in the past. It was a combination of luck, timing, and the fact Caesar was a good politician and a great general that made him the success he was before his assassination. But he would set the stage and the political climate for his nephew and adopted heir to take control of the Roman Republic and become the first Emperor of the Roman empire.

If you have any questions I'd be happy to answer them best I can. If you're interested in Caesar and his life I would recommend Adrian Goldworthy's book on Caesar called "Caesar".