ACT I

A storm breaks out. The priestesses pray the gods not to punish them and to free them at last from their bloody mission. Iphigenia has a recurrent dream: a loving father who, laying his hand on her, finds himself covered in blood, her mother holding a knife and Iphigenia herself raising a knife against her brother Orestes. The storm abates and Iphigenia recounts her nightmares. Cursing her destiny she begs Diana to grant her freedom through death. Thoas, the king of Tauris, tyrannizes Iphigenia. He can no longer sleep and suffers from a persecution complex. He fears death at the hands of a stranger, as an oracle has predicted. To avoid this he demands new human sacrifices. A messenger brings news: two Greeks have been cast up on the shore during the storm. The guards have captured them. Thoas is taken to see them and orders that a sacrifice be prepared. The prospect of this new sacrifice puts Thoas’ court into a state of euphoria.

ACT II

The two Greek prisoners are in chains. In fact they are none other than Iphigenia’s brother, Orestes, and his friend Pylades. Orestes has committed a serious crime: he has killed his mother. He immures himself in silence and curses his fate. Pylades seeks to comfort him. For him, dying alongside Orestes is an honour. The guards separate the two friends. Orestes remains alone and is assailed by the Furies. He is haunted by the memory of his crime. His murdered mother appears before him. The vision vanishes and he realises that it is not his mother but a priestess who has entered his cell. Striking up conversation, both reveal that they are from Mycenoe whilst concealing their respective identities. Iphigenia tortures the Greek prisoner with a multitude of questions about his homeland. She learns sad truths and a lie: Clytemnestra killed her husband Agamemnon upon his return from the war and her son Orestes in turn killed her to avenge his father. Orestes then found deliverance through death. These words confirm Iphigenia’s visions: her family no longer exists. Along with the other priestesses she prepares a funeral ceremony in honour of her dead brother.

ACT III

Iphigenia is anxious. She has grown fond of the prisoner who reminds her of her brother. She decides to save one of the prisoners from death and to entrust him with a letter to her sister Electra who has remained in Mycenæ. Iphigenia explains her plan to the two Greek prisoners. The two friends argue fiercely to decide who shall die to save the other. Iphigenia must choose between them. She hesitates a long time before deciding to free Orestes. Orestes reproaches Pylades for not granting his deepest desire and preventing from him being freed from his crime through death. He threatens to commit suicide thus obliging Iphigenia to modify her decision. In the end, Pylades is freed.

ACT IV

Iphigenia prepares for the sacrificial ritual. She seeks to hide any feelings of compassion or suffering. The priestesses prepare the victim. In the face of death, Orestes thinks once more of his sister Iphigenia sacrificed in Aulis. Iphigenia recognises her brother at the very moment of sacrifice. She does not kill him. Although he killed her mother, she continues to love him. Thoas discovers Pylades’ escape. He feels betrayed by Iphigenia and orders that she and Orestes be slaughtered on the spot. Pylades arrives at the head of a troop of Greek soldiers and kills Thoas. The Greeks have the upper hand in the fighting and intend to kill every last Scythian. The goddess Diana stops the massacre. Orestes begs the gods to forgive him for murdering his mother and prepares to return to Mycenæ with his sister. The Greeks and Scythians joyfully celebrate peace and human dignity.