Horatio the Historian [Richard Haydn] sings to beautiful women about the day that Fabius Maximus [George Sanders] was crowned the dictator of Rome. Fabius Maximus [George Sanders] then delivers a speech about stopping Hannibal’s invasion and searches for his bride-to-be, Amytis [Esther Williams], but she is not there. She and her personal slave, Meta [Marge Champion], visit Rome’s market and witness a slave auction where Varius [Gower Champion], one of Hannibal’s soldiers, is being sold. Since Meta seems captivated by Varius, Amytis engages in a bidding war and wins him.
Varius [Gower Champion] and Meta [Marge Champion] dance and sing in a musical number, If This Be Slavery, and Fabius and his mother, Fabia [Norma Varden], witness the chaotic aftermath. Both scold Amytis, but she dismisses them. It is revealed Fabius and Amytis have been engaged for seven years. Fabius tells her that they’ll be married in a week, or she’ll become a priestess of Vesta. Left alone, Amytis swims in a luxurious private pool, synchronized swimming with living marble statues of Roman gods and heroes, while singing I Have a Dream about finding a better man to fall in love with.
Roman General Scipio [Douglass Dumbrille] interrupts their wedding announcement party to proclaim twelve Roman legions were annihilated by Hannibal, who is twenty miles outside of Rome with war elephants. On the road, Hannibal [Howard Keel] and his vast army sing Hannibal in support of their leader and his goal of defeating Rome. Curious, Amytis and Meta seek out Hannibal but are caught by his soldiers. Horatio the Historian is recording Hannibal’s every movement and word. Amytis [Esther Williams] convinces Hannibal to have a private discussion, but he still orders her execution. Cleverly, Amytis points out Hannibal’s maps are wrong and, although Hannibal sings I Never Trust a Woman, even proclaiming he’d rather trust his pet leopard than a woman, he still goes with her to spy on Rome.
When Amytis directs Hannibal to cross the Tiber River to take a closer look at Rome's fortifications, Hannibal admits he can’t swim. While she teases Hannibal, the two float across with Amytis leading him by the chin. However, it turns out there is a bridge, and Hannibal, in irritation, has them go back for his armor and the chariot. The pair are filled with romantic tension; Hannibal sings to Amytis Dont Let This Night Get Away about how they should be together tonight. Just as they are about to kiss, Romans discover their chariot, and Hannibal fights and kills several Roman soldiers before taking Amytis captive again and riding back to camp.
Furious, Hannibal demands Amytis’ execution, thinking she betrayed him, but Amytis declares she only came to his camp to see him, the man she’s been dreaming of. Even though Hannibal promises to kill her tomorrow and Amytis says she understands, they kiss passionately instead.
During a reprise of Hannibal, his armies approach Hannibal’s tent to start the invasion of Rome, but instead find him infatuated with Amytis. When the armies ready for a later attack at high noon, Hannibal dismisses this men again, rescheduling for dusk. Bored and frustrated, Horatio the Historian records that Hannibal is “reconnoitering,” while Hannibal and Amytis leisurely enjoy his treasures. When Varius suddenly reappears and returns to his original position as Hannibal’s elephant keeper, he explains there are only two Roman legions left to defend the city. Amytis pushes Meta to stop Varius from telling more. As Meta grows offended by Varius talking about owning her as a slave, the pair sing a training-number while the performing synchronized choreography with Hannibal’s war elephants, including a baby elephant. Although Amytis also admires Hannibal’s elephants, she suggests they be brighter in color.
When Fabius arrives in a negotiation delegation to Hannibal’s camp, he gives his medallion with Amytis’ image inside, leading Hannibal to discover Amytis’ identity, much to his fury. Intent on Meta being his wife in Carthage, Varius frees her, but Meta refuses to leave Amytis, so she knocks out Varius, allowing both women to escape. When chased to a cliff, Amytis rides her horse off the edge and into the water. Three of Hannibal’s soldiers dive in after her, following her into a sunken boat and further into watery depths. She escapes them and safely arrives in Rome, joining Fabius but instead deciding to become a Vestal priestess rather than marry him.
Hannibal lays siege to Rome, and the two armies engage in combat, including the war elephants equipped with a battering ram to break the gates. To avoid slaughter, Fabius surrenders, but Amytis petulantly urges him to keep fighting. When Fabius offers tribute, Hannibal asks only for Amytis. She graciously accepts, pretending to sacrifice herself, as she prefers to join Hannibal rather than to stay in Rome. Initially Hannibal rejects her to tease Amytis, but he quickly relents, bringing her with him. As they leave Rome together to return to Carthage, Hannibal reveals he has painted all of the elephants vibrant colors for Amytis.
