The evening before the Trojan War. The Greek armies have assembled in Aulis under their supreme commander Agamemnon. An absence of wind means the fleet is unable to sail to Troy. A seer advises Agamemnon to entice the goddess Diana to end the calm by offering his eldest daughter as a sacrifice. Agamemnon orders Iphigenia be brought from her home in Mycenae under the pretext that she should wed the warrior Achilles, and her mother Clytemnestra acquiesces. The bride finds herself on the sacrificial altar, where she loses consciousness before waking to discover she is on the distant Tauris peninsula. In the final seconds, the goddess exchanged her with a doe. Agamemnon slices the animal’s throat, believing he is sacrificing his own daughter. The wind picks up, and the Greeks can begin their ten-year war against the Trojans. Many years later. During her involuntary exile, Iphigenia serves at the side of other Greek women as a priestess in the Temple of Diana. Her task is to sacrifice every stranger who sets foot on Tauris to the goddess. Regardless of the traumatic events in Aulis and the years that have elapsed, the longing for her home and family has not diminished.
A storm breaks. The priestesses beg the gods to spare them and finally release them from their bloody sacrificial task. However, even as the storm abates, Iphigenia is still troubled. She has recently dreamt of her family, and of her affectionate yet unrelenting father. Of the destruction of her homely palace. Of her mother chasing her blood-covered father with a knife. Finally of stabbing her own brother Orestes with her own hand. Iphigenia is afraid of knowing the significance of these dreams. She shall never see her family again. She curses her fate and pleads with the goddess Diana for salvation via a speedy death. Thoas, ruler of Tauris, forces Iphigenia to conduct further sacrifices. He has been troubled by fear of death ever since an oracle announced to him that he would die at the hands of a stranger. A messenger tells of the capture of two shipwrecked Greeks. Thoas orders the preparation of the victims.
Two Greeks are lying in chains. They are Iphigenia’s brother Orestes and his friend Pylades. Orestes is suffering from heavy feelings of guilt due to killing his mother. He also blames himself for putting his friend in danger, but Pylades attempts to console him. To die together with Orestes would be, for him, the fulfilment of his burning desire. The guards drag the friends apart. Orestes falls exhausted to sleep and is tormented by visions of the Furies, who continually remind him of the murder. His dead mother appears. He awakens, and recognises that it is a priestess who has entered his cell to ask him about his origins.
Upon learning that the prisoner comes from Mycenae, she bombards him with questions about the events in his homeland. She hears cruel truths and a lie: King Agamemnon was killed by his wife Clytemnestra after his return from the war, resulting in Orestes avenging his mother’s death. Orestes is said to have found the desired redemption in death. Iphigenia sees her worst fears confirmed: her family has been wiped out. Together with the other women, she holds a funeral service for her deceased brother.
Iphigenia feels affection for the young Greek, who reminds her of her brother. She summons both prisoners and submits a plan to them: she can help one of them escape. This one should take a message to her sister Electra in Mycenae, the other must be sacrificed. The friends vie with each other for the honour of dying so that the other may be spared. Iphigenia hesitates before finally revealing what she has already decided: Orestes should go free. He accuses Pylades of depriving him of his one desire: that his death shall free him from his guilt. He threatens Iphigenia with suicide and pressures her to reconsider. She allows Pylades to go free.
Iphigenia prepares herself for the sacrificial ritual and tries to extinguish any feelings of sympathy inside. Upon the sacrificial altar, Orestes laments his sister who, years before in Aulis, died in the same manner. Iphigenia recognises her brother as she wields the knife. She does not kill him and refuses to sacrifice any more victims. Thoas, who has been informed of Pylades’ flight, demands the death of the siblings. Pylades storms the scene with Greek soldiers and kills Thoas. The goddess Diana intervenes again. She prevents a Greek massacre of Thoas’ people and proclaims the will of the gods: Orestes receives atonement for killing his mother. He shall return to Mycenae with his sister. Peace and humanity are celebrated.