The story begins with an unnamed Thracian's involvement in a campaign against the Getae (Dacian tribes, in what today is Romania) under the command of the legatus, Claudius Glaber. In 72–71 BC, Roman general Marcus Terentius Varro Lucullus, proconsul of the Roman province of Macedonia, marched against the Getae, allies of Rome's enemy, Mithridates VI of Pontus. The Getae frequently raid the Thracians' lands to the south, so the Thracians are persuaded by Glaber to enlist in the Romans' service as auxiliaries. Glaber, persuaded by his wife Ilithyia to seek greater glory, decides to break off the Getae campaign in order to confront the forces of Mithridates in Asia Minor. The Thracian preferring to protect his homeland as promised, feels betrayed and leads a mutiny against Glaber, but returns to find his village in flames. The Thracian finds his wife Sura, but they are captured by a vengeful Glaber the next day; the Thracian is condemned to die in the gladiator arena, while Sura is condemned to slavery.

The Thracian is shipped to Capua in Italy, a center of gladiator training. Against all odds he slays the four gladiators appointed to execute him in the arena and becomes an instant sensation with the crowd. Senator Albinius commutes the punishment from death to slavery. The prisoner's true name unknown, Lentulus Batiatus, the owner of a ludus in Capua, suggests the name "Spartacus" because he fought like the ferocious Thracian king of that name. Noting well the Thracian's fierce raw talent and popularity with the masses, Batiatus purchases him for training within the walls of his ludus under the tutelage of the doctore (or instructor) Oenomaus, a former gladiator and fellow slave. He is befriended by Varro, a Roman who sold himself into slavery to pay his debts and support his family. He is harassed by more senior gladiators, notably Crixus, an undefeated Gaul, and Barca, a Carthaginian. Spartacus soon learns that Sura was sold to a Syrian slave trader. Batiatus, who has been unable to control Spartacus during his first days of training, returns a makeshift garter of hers, and promises to find Sura and reunite them in exchange for his cooperation in the arena.

After many near-fatal ordeals and much further training, Spartacus attains the status of a living legend and is named the "Champion of Capua". Batiatus arranges the purchase of Sura, but she is delivered mortally wounded, supposedly having been waylaid by bandits en route. Her murder was secretly ordered by Batiatus to keep Spartacus loyal and focused. Spartacus casts off his heritage as a Thracian and forgets his dream of freedom, becoming content with life as champion.

The turning point comes when Spartacus is set to fight his only friend in the ludus, Varro, in an exhibition match celebrating the coming to manhood of the Capua magistrate's son, Numerius. Ilithyia, who has hated Spartacus since he embarrassed her husband Glaber by his mutiny, seduces the young man and convinces him to demand death for the loser of the match. Spartacus wins (as expected), and when the young man gives the "thumbs down", Batiatus, wishing to ingratiate himself with the boy's powerful father, forces Spartacus to comply and kill Varro. Suffering from both a wound received during the match and his remorse over having to kill his friend, Spartacus has feverish dreams that lead him to suspect that Batiatus arranged Sura's death. He is later able to confirm his suspicions. Knowing that it is all or nothing when it comes to resistance of his enslavement, he resolves to "kill them all" and lead a revolt against the ruling house he once fought for.

In order to get his revenge, Spartacus enlists the help of Crixus and the rest of the gladiators to defeat the house of Batiatus once and for all. A battle to the death between Crixus and Spartacus is arranged for the Capuan elite at the ludus. The doctore, Oenomaus, confronts Batiatus about Barca's death and Ashur's hand in it. Spartacus gains support from Mira, who agrees to surreptitiously open the gate to the villa from the training area. Crixus initially refuses to aid Spartacus in the hope of being reunited with Naevia. However, after learning during the fight that he has been deliberately drugged to ensure Spartacus' victory, he helps Spartacus get within reach of Batiatus. At the first attack, the doctore Oenomaus prevents Spartacus from killing the lanista. In the ensuing chaos, the gladiators kill the guards and some guests. Crixus persuades Oenomaus to join him with Spartacus; Ilithyia flees and orders her guards to protect her by sealing off part of the ludus. Oenomaus, fulfilling his word, tries to kill Ashur, but Ashur barely manages to escape. Crixus grievously wounds Batiatus' wife, Lucretia, with a sword stab to her abdomen, piercing her womb and killing their unborn child. Aurelia slays Numerius after revealing to him that Varro was her husband. Spartacus finally kills Batiatus in front of the seriously wounded Lucretia. After the massacre, Spartacus vows to make "Rome tremble".