After defeating Glaber and liberating slaves from the mines the rebel army has grown into the thousands. They defeat a Roman army under commanders Cassinius and Furius but cannot capture them. Spartacus is wary of Gannicus’ lengthy celebrations while the common man in the camp begins to feel distant from their Godlike leader. Senator Metellus is sent to ask Marcus Crassus to raise ten thousand men to fight Spartacus. Crassus agrees to fight under Cassinius and Furius but his messenger is captured giving away their location. Spartacus takes the heads of both men while Crassus continues training with a former gladiator Hilarus.

Spartacus asks Theotokos to tell him about the defences of the city where he lived (Sinuessa en Valle). Out of fear the Aedile of the city has disarmed the population and insisted on a curfew. Spartacus, Gannicus and Crixus enter the city as merchants and witness a stoning. Spartacus pretends to buy grain from the Aedile and his wife while Gannicus contacts an old friend who can manufacture two swords. At night Spartacus and Gannicus open the gates and the rebel army storm in. Back in Rome Crassus recruits a young Julius Caesar for his army but gives the subordinate command to his son. He also insists that his wife stays behind and admits his love to Kore.

Crixus makes two Romans fight over a scrap of bread as many of the rebels question why the Romans still live. Spartacus tells Laeta that he will treat the Romans well if she will help him. Cilician pirates arrive asking for the seal of the Aedile who they had a deal with. Spartacus offers to buy grain from them and they arrange an exchange. A slave girl who Gannicus saved offers herself to him but he turns her away. Tiberius hears of Sinuessa’s fall and hurries to the scene. He leads an attack when he sees Spartacus meeting with the pirates. He is wounded as Heracleo proves himself to Spartacus. In the city Naevia accuses Attius.

Spartacus negotiates for more grain with Heracleo while Crixus urges him to kill their Roman prisoners to ease their supply burdens. A small group of Romans infiltrate the city and although they are swiftly cut down Caesar manages to convince Spartacus that he is a slave. He soon makes common cause with Nemetes and kills a Roman woman he had enslaved, claiming he desires all Romans in the city to be killed. Laeta’s small group of friends are discovered by Gannicus who attacks Crixus and Naevia in revenge for Attius’ death. Caesar encourages the tumult until Crixus invites a general slaughter. Meanwhile Crassus disciplines Tiberius’ detachment with the arcane punishment of Decimation. Kore encourages him to see Tiberius as a man and so he includes him in the punishment.

Spartacus leaves for Sicily with the Cilicians and Gannicus. They capture some grain intended for Crassus' troops but Crixus is furious that he wasn't consulted. When Spartacus returns he explains that he has a plan to divide and crush Crassus' legions. He releases Laeta and feeds her false information intended for Crassus. However Crassus has paid off Heracleo and his men surprise Spartacus at the docks. Caesar kills Nemetes and attempts to open the gates.

Crassus' men occupy the city as Spartacus pushes his people out of the north gate. Gannicus and Donar agree to create a distraction and find Sibyl as they set fire to the city. Donar is captured and he and the remaining slaves are prepared for the Carnificina in honour of Caesar's victory. Laeta is restored to her former beauty but then handed to Heracleo as part of the deal he struck. She is branded as his slave but Gannicus and Sibyl free her. Meanwhile Tiberius threatens Kore so that she won't reveal what happened to Crassus. Caesar teases Tiberius about his diminished status and at the Carnificina Tiberius attempts to embarrass him by setting Donar free. Gannicus and his two charges make it safely to the snowy ridge only to find that Crassus has built a wall to trap the rebels there.

Tiberius is restored to command and Kore told that she will remain in Sinuessa with him after the war. She asks Caesar to help her but when Crassus makes it clear how much he loves his son she flees to the rebellion. Meanwhile Crassus' troops make camp near the ridge and wait out a passing storm. The rebels huddle for shelter while Spartacus and Crixus argue over their strategy. Gannicus and Sibyl take shelter together and have sex.

Crixus wants to march on Rome while Spartacus aims to leave Italy. After taking one last Roman settlement the two groups say their goodbyes. Meanwhile tensions remain high between Caesar and Tiberius as they pursue. Crixus, joined by Agron and Naevia defeats the legion guarding Rome but is then crushed by Crassus.

Spartacus’ group encounter the scouts of Pompey’s army. Other scouts then arrive at Crassus’ camp asking for a meeting. Caesar advises that Tiberius be sent. It turns out to be a trap set by Spartacus who takes Tiberius’ men and has them fight as gladiators to honour Crixus’ death. Naevia has returned with Crixus’ head and is ready to kill Tiberius. Caesar soon arrives offering to swap Tiberius for five hundred prisoners including a crucified Agron. Naevia makes the deal but Kore kills Tiberius. She offers herself instead and the deal goes through.

Spartacus spreads confusion to try and throw Pompey off his scent. He also prepares for the final battle, sending the women and children toward the Alps. Meanwhile Crassus finds out the truth about Tiberius and Kore and forgives her. Spartacus asks Gannicus to lead a part of the army. Crassus asks Spartacus for a private conversation before the battle. The battle sees almost all the rebels fall. Spartacus nearly kills Crassus but lives long enough to die a free man. Gannicus joins Kore on the cross. Agron and Nassir lead what remains of the rebels out of Italy.