This scene takes place in front of the royal palace in Mycenae (in Ancient Greece).
The old slave begins by addressing his companion, Orestes, as the son of Agamemnon. He gives us a recap to bring us up to speed:
When Orestes was a young boy, Agamemnon was murdered by his wife Clytemnestra and her lover Aegisthus. After the murder, the two took over the throne. Orestes's sister, Electra, gave her baby brother to an old slave to smuggle out of town. She wanted her brother to live so that he could grow up and one day come back to avenge their father.
And now, it's time for the avenging.
Orestes is back in town with his buddy, Pylades, and ready to spill some guilty blood. The old slave urges his master to action.
Orestes congratulates the old slave on his loyalty. Orestes reveals that he's been to see the Delphic oracle, who told him that justice was ready to see her purpose done, that blood would be shed and victory won. Orestes interprets this is as a green light to slay Aegisthus.
Orestes isn't just talk – he's a man with a plan. He instructs his slave to go into the palace and "reconnoiter," (i.e., get some information), and come back with a report. Orestes further instructs the slave to pretend that he's a stranger from Phocis sent by their military ally to give the news that Orestes is dead from a chariot-racing accident.
Orestes figures that because it's been so long since the old slave has been in town, no on will recognize him in the palace.
Meanwhile, Orestes and Pylades plan to pay their respects to Agamemnon's grave. Orestes explains that, as is the custom, he will place a lock of his hair on the grave.
Orestes takes a moment to ask the gods to bless his mission, and sends the slave on his way.
Suddenly, from offstage we hear the sound of Electra lamenting her lot in life. Pylades suggests that they hang out for a minute to listen to her laments, but Orestes insists they go pay their respects to his father's grave, because that is what Apollo told him to do.
All three men exit.
Electra enters from the palace to deliver a smashing monologue.
She is not a happy girl. Since her father was murdered she's been grieving and lamenting his death. But with his killers on the throne – one of them her mother – the throne she's not exactly in a great spot. They treat her like a slave because she refuses to play nice.
Electra prays to the gods to send the Furies after her mother. (Note: the Furies are scary female creatures who torment the guilty. They are basically vengeance in monster-form.) Electra also prays that they send Orestes to her, as she is weak alone and cannot bear the burden of so much suffering by herself.
The Chorus enters. (The Greek Chorus is a stock part of Greek Tragedy. It's a group of a dozen-or-so actors who sing, get the audience up to speed on background information, comment on what's going on, and help interpret the play.) In this case, the Chorus is a group of Mycenaean women.
The Chorus have a conversation with Electra.
The Chorus wants to know why Electra is still grieving for her dad when, he was killed so long ago. They agree with her that it would be nice for Aegisthus to die as punishment, but all this moping about isn't going to fix the problem.
Electra knows they are on her side and are trying to make her feel better, but she explains that it's her filial duty to grieve for her father. (In other words, Electra believes that as Agamemnon's daughter, she has the responsibility of grieving for his death.)
The Chorus points out that grief won't bring Agamemnon back. They add that Electra's sisters, Chrysothemis and Iphianassa, have moved on to other things. Besides, they say, Zeus will send Orestes home soon, and he'll take care of everything.
Electra laments that she is still waiting for Orestes. With no child and no husband, her whole life is consumed with this game of grieving and waiting.
She's frustrated that Orestes keeps sending messages saying that he's coming soon, but has yet to make good on this promise.
The Chorus tells her not to worry: Zeus sees all, and he will surely send Orestes their way soon. Time is a god of healing, they tell her.
But Electra is getting tired of being patient. Her life is withering away to nothing. She recounts with anger the night that her father was killed, and rages that his killers live such a life of splendor now.
But the Chorus maintains that her wretched state is her own fault. She needs to accept that there's nothing she can do about the situation and move on already.
Electra counters that she has no choice; "their crimes dictate my actions" she says (221-222). She insists that her father's killers pay for blood with blood.