Returning to Rome after a victorious campaign, Licinius finds his beloved Julia has become a priestess of Vesta. Although Julia attempts to avoid going to Licinius's triumph, she is delegated to present him with a wreath. He tells her that he intends to kidnap and reclaim her.
In the temple of Vesta, Julia guards the eternal flame and prays to be freed of temptation. Licinius arrives; during their rapturous reconciliation, the flame expires. Licinius is advised by Cinna to flee. Julia is interrogated by the High Priest but refuses to name Licinius. She is sentenced to death for licentiousness.
Despite the pleas of Licinius, Julia is to be buried alive; even when he admits his intrusion to the Temple, Julia claims not to recognise him. A thunderstorm ensues, during which lightning reignites the sacred flame. Recognising this as a sign from the Gods, the High Priest and Vestal Priestess release Julia who is then married to Licinius.