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. He also loses all of his money in a crooked dice game leading to a major brawl. For Vorenus, he will have a reunion with his wife Niobe who he has not seen for 8 years. He's told that the baby he finds in his home is his grandson but Niobe is hiding a secret. In the Senate, there is a move to have Caesar declared a traitor but when Mark Antony tries to return to the Senate to veto their decision, Pullo is attacked by someone he fought the night before. Antony thinks the attack is against him and Pullo kills the man and Caesar declares Pullo a hero.

Atia and her family have stayed behind when Pompey and others fled and she now throws a party for her triumphant uncle, Julius Caesar. She clearly has her sights set on the great leader and is puzzled when he sends her a guest list that includes Servilia of the Junii. She soon finds out why. Pompey wants to find out what happened to the gold from the Roman Treasury and sends his son Quintus to Rome to find out what happened. They go directly to Vorenus' home but he has no idea what they are talking about. Pullo arrives however and Vorenus tells him to go directly to Caesar himself and explain. Octavian meanwhile learns of one of his uncle's secrets.

Caesar contemplates Pompey's counteroffer. 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.

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 step to manhood and orders Pullo to take him to a brothel so he can have his first sexual experience. Atia also continues with her scheming ways and believing that Caesar is done for, decides she had better make friends with Servilia.

The defeated Cato and Scipio fall back on the African city of Utica after the Battle of Thapsus where they decide to end it all. Caesar, after two years of fighting in Greece and Egypt, returns to Rome and receives a hero's welcome. Meanwhile, Servilia's cold rage against the Julii clan makes Brutus's submission to Caesar even more painful. Octavian returns home from military school and Caesar, impressed with his nephew's incisive political acumen, appoints him a pontiff despite his youth. Having opened and operated a profitable butcher shop, Niobe and Lyde get the reluctant Vorenus and Pullo to join the trade, but Vorenus again crosses paths with the thug Erastes, now the crime lord of the Aventine. Learning of Caesar's secret "affliction," Servilia persuades her lover Octavia to cajole her brother into revealing more, but she only learns Niobe's secret instead. Servilia motivates Octavia to try again by other means, with dreadful consequences for both sister and brother. Pullo's affection for his slave Eirene deepens. Enraged at Servilia's manipulation of her children, Atia enlists Timon and his band of thugs to retaliate, thus escalating the term 'catfight' to a very different level.

The price of Caesar's mercy: Cicero nominates Caesar to an unprecedented ten-year dictatorship and Brutus speaks in support of the motion. With martial authority and Niobe at his side, Vorenus campaigns for magistrate under Posca's advice, but is shocked to learn from Posca that Caesar has already fixed the election in Vorenus's favor. Meanwhile, Atia continues her humiliation of Servilia while denying any involvement in her assault. But Atia becomes troubled by the silent depression of Octavia after Octavian compels her to return home from the cloister where she had fled. As Servilia lies at home shattered by her recent attack, she soon revives and gets her self-confidence back when she takes in the homeless and embittered Quintus Pompey whom she sees as her tool for revenge against Caeser for leaving her. As Caesar prepares for his Triumph involving five days of celebration and games, Antony finds that the dictator has no sense of humor about the trappings of power. The circulation of a denunciation of Caesar, signed by Brutus, fascinates Rome but stuns Brutus, who suspects his mother. Denied permission to march with the Thirteenth in the Triumph, the dejected Pullo resolves to make a new life as a civilian with Eirene, but his dream leads only to horror for the Vorenii and utter wretchedness for himself.

Rejected by Vorenus and Eirene and racked by guilt for the killing of Eirene's fiancé out of a jealous rage, Pullo has sunk to working as an assassin for the gangster Erastes. When Pullo gets arrested for killing one of Caesar's popular opponents, he condemns himself by refusing to name who hired him, despite Octavian's attempts to defend him. Meanwhile, Vorenus finds his new official duties as magistrate tedious, especially when he gets caught between Caesar and the demands made by veterans' spokesman Mascias. Niobe revels in the prestige of Vorenus's office until Caesar invites the Voreni to a symposium at Atia's house. Despite Servilia's surreptitious propaganda depicting Brutus as a tyrant-killer, and the urgings of Cassius and his own doubts, Brutus resists turning against Caesar. Antony makes his move to win back Atia. On the point of death in a gladiator arena, Pullo finds a new reason to live that yet again puts Vorenus in a tight spot. Also, Caesar makes a move that compels the conflicted Brutus to make up his mind to turn against Caesar.

Vorenus' defense of Caesar lands him in an unexpected position of power within Rome. Meanwhile, Servilia hurls the final obstacle in her ambitious and complex revenge plan against Atia.

In the wake of Caesar's death, Mark Antony considers a move north, while Vorenus issues a curse he soon regrets.

Even though his wife and children are avenged by the Erastes killing, Lucius Vorenus keeps mourning for over a month till Pullo gets Marc Antony who scolds him for Caesar's death and the continuing bloody Aventine gang riots that have resulted in the gangs wanting to fill the void left by Erastes sudden demise. Octavian is losing patience with Marc Antony for payment of Caesar's inheritance. Meanwhile, Queen Cleopatra of Egypt arrives in Rome to pay her respects to Caesar and she also negotiates with Antony's military protection for her Pharaonic throne in exchange for valuable grain shipments. But she gets dismissed as a whore when she demands that her four-year-old son, Caesarion, be recognized as Caesar's legal son. Yet the uninvited pair of them is welcomed by Antony at Atia's party. Abusing a truce in the name of the goddess Concord and smashing up her statue, Vorenus imposes as 'son of Hades' on the gang captains a peace, paid off by Antony so trade and politics on and near the Aventine no longer get disrupted. After his mother Atia and sister Octavia tell him to accept Antony denying Caesar's legacy and laugh at his ambition to provide Rome the leadership it needs, Octavian borrows against his vast inheritance to buy popularity by paying for Caesar's lavish bequests to the populace; Antony violently refuses a political deal with him. Octavian then leaves home and retires to Campania with General Agrippa. Cicero and Brutus' mother, Servilia, hope this strife among the Julii clan will allow their party to return to Rome. Also, Timon's long-lost brother, Levi, arrives back in Rome wanting his help to make a new life for himself.

Lucius Vorenus, the power-hungry "Son of Hades", controls the Aventine but practices a pointless, beastly reign of terror, coming down hard on gang captains for futilities, and nearly ruins his friendship with Pullo, whose efforts to calm things down are mistaken for disrespect and disobedience, even starts a fight once he learns the truth about Niobe; Pullio leaves Rome disgusted. After Atia convinces Marc Antony the governorship of ghastly Macedonia after his consulate would not only be unpleasant but leave him exposed to his dangerous enemies, he puts the heat on senatorial leader Cicero to give him Gaul instead, which once was the base for Julius Caesar's coup d'état. The slave Duro endures male prostitution but most arrogantly demands extra pay and even a kiss from Servilia as it will take more time to commit the planned murder in Atia's home. Marc promises Atia not to hurt Octavian, whose recruiting he calls a joke, after putting down his party's expected plot. Brutus has a hard time controlling himself while soliciting the Bithynian king's financial support to raise an army. Instead of proposing Antony for governor of Gaul, Cicero sends an extremely insulting speech and joins Octavian's growing army.

Having learned that Vorenus' children are alive, Pullo sets off to find him in Gaul where he is again a serving soldier in Mark Antony's army. He had hoped to arrive before Octavian and Antony's armies meet in battle. Too late however, he is forced to find what is left of Antony's army in the mountains. He finds Vorenus alive and well, if somewhat battle worn, and they set off to find the children. The victorious Octavian plans his return to Rome. In Western Turkey, Brutus and Cassius amass their own army, now 9 Legions strong. In Rome, Servilia's attempt to kill Atia fails and Atia has her kidnapped tortured beyond what even her henchman Timon can stand.