Act 1:
Licinius has returned home from the war as a victorious Roman general. He encounters Cinna who wants to know why he is so sad. Licinius confesses that he is in love with Julia and that five years previously he was unable to prove to her father that he was worthy of her. It was to improve his situation that he joined the army. After his return he learned that Julia was forced to promise her father on his deathbed that she would become a Vestal Virgin and preserve her chastity. Cinna agrees to help Licinius and the two men reaffirm their friendship.

The Vestal Virgins sing to their goddess and the eternal flame that they guard in the temple. The Great Vestal condemns to death every virgin who breaks her vow of chastity. To celebrate Rome’s victory in the war she announces a triumphal procession. Julia is given the task of crowning Licinius with the “wreath of immortality”. Left alone, Julia is torn between her joy at seeing Licinius again and her fear of the consequences of her forbidden love.

During the festivities, the Great Vestal chooses Julia to guard the eternal flame in the coming night. Licinius hears about this and tells Julia of his plan to abduct her from the temple. A consul, the High Priest and the entire population celebrate the triumphant warrior.  

Act 2:
At night in the temple, Julia begs Vesta for mercy. She wishes to see Licinius one more time and then surrender herself to the gods’ vengeance. In front of the altar, Licinius and Julia swear their love in a fever of passion. The eternal flame goes out. Cinna enters the temple and tries to persuade Licinius to flee. But Licinius refuses to comply with either Cinna’s or Julia’s urgings to leave.

When voices are heard from outside, Licinius and Cinna depart. The people and the other Vestal Virgins swarm into the temple and condemn the crime that has been committed. The High Priest demands from Julia the name of the intruder, but she refuses to reveal it. He curses her and sentences her to death.

Act 3:
Cinna tells Licinius that he has put together a troop of legionnaires to assist him. Licinius tries unsuccessfully to persuade the High Priest to overturn the death sentenc and confesses that he is Julia’s lover. The Chief of the aruspices points out the gathering soldiers to the High Priest and recommends delaying the sacrifice. However, the High Priest rejects this idea. Before the death sentence is carried out, he has Julia’s veil placed on Vesta’s altar. If the veil catches fire it will mean that Vesta forgives her priestess. Licinius publicly admits that he is the guilty party and demands that Julia’s life be spared. But Julia pretends not to know him. Suddenly a storm breaks out, and a lightning bolt sets fire to Julia’s veil. The High Priest proclaims a miracle and Vesta’s forgiveness.