The film chronicles Allen's career - from teen writer to Sid Caesar's TV scribe, from stand-up comedian to award-winning writer-director averaging one film-per-year for more than 40 years. Exploring Allen's writing habits, casting, directing, and relationship with his actors first-hand, new interviews with A-listers, writing partners, family and friends provide insight and backstory to the usually inscrutable filmmaker.

Caesar winters his army in Gaul near the Italian border while his enemies in Rome fear that he will do something no Roman General has done: cross the Rubicon with his army. To counter-balance his opponents, Caesar puts his friend Mark Antony up for office as the people's Consul. Vorenus and Pullo accompany Mark Antony and Octavian to Rome. For Pullo, it's an opportunity to get drunk and ravish every woman in sight.

Caesar pursued Pompey to Greece but the tide has turned and it's Caesar who is on the run. He contacts Mark Antony, who he left in charge in Rome, to come and join him with the 13th Legion but Antony seems to be in no hurry.
Vorenus has re-enlisted in Antony's Legion and he and Niobe have begun to renew their marital relationship. The presence of Niobe's sister is the only sour note in their house. Pullo meanwhile continues to train young Octavian in the use of arms and the boy's mother Atia is so pleased with his development that she decides he should take another.

In episode two, we discover the golden age of the La Tene Celtic warrior and reveal how their world extended as far as central Turkey. But by the middle of the first century BC, the Celts were under threat from an expanding Roman Empire, and the Gallic warrior Vercingetorix would challenge Julius Caesar in an epic battle that would shape the future of Europe.

Caesar contemplates Pompey's counteroffer but Mark Anthony wishes the war. Vorenus continues to struggle as a businessman and must reevaluate his career choice. Atia schemes to come between Caesar and Servilia and Pullo seeks Octavian's help.

With Caesar quickly advancing toward Rome, Pompey begins ordering a retreat and forces his citizens to pick sides. Timon does Atia's dirty work and Vorenus cannot understand why no one is resisting while on a scouting mission.