The Rivalry
While King Mitridate is away fighting the Romans, his two sons have both fallen in love with Aspasia, the king's betrothed. Sifare, the younger son, suffers in tortured silence — he loves Aspasia but will not dishonour his father. Farnace, the elder, has no such scruples: he openly courts Aspasia and has secretly allied himself with Rome. Aspasia herself is trapped: she returns Sifare's love but is bound by duty to the absent king. The governor Arbate tries to keep the peace, but the brothers' rivalry is spiralling toward catastrophe.
Mitridate's Return
Mitridate returns from war crowned with laurels — but the victory abroad cannot mask the betrayal at home. He senses immediately that something is wrong. Arbate informs him of Farnace's treachery: his eldest son has been wooing Aspasia and conspiring with Rome. The king's homecoming turns bitter. Meanwhile, Ismene, the Parthian princess promised to Farnace, watches her fiancé ignore her and pursues the other woman. She bears the rejection with quiet dignity.
Suspicion and Test
Mitridate confirms his suspicions about Farnace and explodes with rage. But the king's fury is calculating as well as hot — he devises a cruel test for Aspasia, pretending to release her from their engagement to see if she will reveal her true feelings. Farnace, caught out, begins to feel the first pangs of guilt. The political alliance with Rome that seemed so clever now looks like a noose.
Sifare and Aspasia
Sifare and Aspasia meet for what they believe may be the last time. Sifare must leave — his father's suspicion is growing — and the farewell is devastating. He sings the opera's most beautiful aria, finally revealing the depth of his love. Aspasia, left alone, wrestles with her impossible situation in music of extraordinary emotional power. The two most sympathetic characters in the opera are being crushed by forces beyond their control.
Mitridate's Fury
The full truth emerges: both sons love Aspasia. Farnace confesses his guilt, but it is too late for confession to help. Mitridate, betrayed by his own blood, strips himself of all mercy. He condemns Aspasia to death and declares that neither son will be spared. The king's rage is total and terrifying — the warrior who faced Rome's legions without flinching is undone by the treachery of his own family.
The Lovers
With death looming, Sifare and Aspasia have nothing left to hide. They declare their love openly in a duet of heart-breaking tenderness — if they cannot live together, they will face whatever comes side by side. It is the emotional climax of the opera: two people choosing love over survival, their voices intertwining in music that transcends the conventions of opera seria.
The Battle
The Romans attack. Mitridate, despite everything, rides out to face his lifelong enemy one final time. Sifare, proving his loyalty through action, fights at his father's side. Even Farnace, transformed by guilt and Ismene's patient love, turns against his Roman allies and joins the battle. Marzio's final temptation falls on deaf ears. Aspasia, believing all is lost, contemplates taking her own life rather than submit to a forced marriage.
Reconciliation
Mitridate is carried back from the battlefield, mortally wounded but victorious. In his final moments, the dying king does what seemed impossible: he forgives both sons. He blesses the marriage of Sifare and Aspasia, recognises Farnace's redemption, and dies declaring that Pontus will never yield to the Capitol. The fourteen-year-old Mozart turned a conventional lieto fine into something genuinely moving — a father's last gift to the children who failed him.