Orestes returns from years of exile to visit the grave of Agamemnon, his father, who was murdered by his mother, Clytamnestra. He is accompanied by Pylades, who remains silent until much later in the play. He opens the play with an invocation to "Cthonic Hermes", who acts as a messenger between the Olympian gods and the Underworld. He asks Hermes to stand by him and "guard the fathers' power." Orestes has come to give proper mourning to Agamemnon, as he was not present for his burial.

This invocation breaks off after five lines, and there is a significant chunk of text (perhaps eighty lines) missing from the only remaining manuscript of the play.

Orestes offers a lock of his hair to Inachus, the river-god of Argos. This is in thanks for his nurture, as river gods were worshipped as givers of life. He then lays second lock on his father's tomb, as an offering and token of grief.

As he is laying down these locks, Orestes catches sight of a group of black- robed women, the chorus, moving towards the grave. He wonders whether they are mourning some new sorrow of the house, or whether they have also come to do honor to Agamemnon. Orestes recognizes Electra, his sister, among the women, conspicuous by her bitter mourning. Orestes calls Pylades to hide with him, so that they may observe the women in secret.

The chorus of women then sings that they have been sent from the palace to bring libations to the dead. They are beating their breasts and tearing their cheeks and clothing. They explain that they have come as a result of a terrible dream that queen Clytamnestra had the night before. The dream interpreters said that the dream came from the dead king, who rages against his murderer. The queen then bid the slave women go to the grave and give libations, in hopes of abating his anger. But the women are afraid to speak for her, as there is no redemption for a house once blood has been spilt.

They say that, while some worship success more than the gods, they will pay for their crimes in the end. Once blood has been spilt, it will not seep into the ground, but clots and seethes like an infection in the minds of the guilty. Blood cannot so easily be washed from a polluted hand. As slaves, they must obey their masters, but the women weep behind their veils.