King Mitridate has left his empire in the care of his sons Sifare and Farnace while he is away at war. Deceived by a rumour of his father's death, Farnace declares his love to the King's betrothed, Aspasia. She seeks the protection of Sifare. Mitridate returns with Ismene as a bride for Farnace. When he hears of Farnace’s guilt, he determines to kill him. Will the ensuing intrigue of rivalry - in love and in politics - wind its way to a happy end?