Clytemnestra enters with an attendant from the palace and immediately begins insulting Electra. The Queen says it's Electra's fault if she (Clytemnestra) says horrible things to her. Anything that Queen Clytemnestra says is only in retaliation to the horrible things Electra says about her.
Clytemnestra then proceeds to defend her murder of Agamemnon. She reminds Electra that he sacrificed one of her other daughters, Iphigenia, to the gods, in order to get his army's ships home safely from Troy. What right did he have to do that? For that reason she doesn't regret murdering him at all. Justice was on her side.
Justice doesn't have anything to do with it, says Electra. The point is that Clytemnestra murdered her husband. Besides, it wasn't justice that drove her to do the deed – it was Aegisthus.
Then she explains her father's decision to sacrifice Iphigenia. He was out hunting and inadvertently angered the goddess Artemis. She forced him to sacrifice Iphigenia as penance. Because he sacrificed his daughter out of duty to the gods, it wasn't his fault.
And even if it were, does that really justify Clytemnestra killing him in retaliation? By that eye for an eye standard, Clytemnestra should be ready to die herself.
And besides, continues Electra, none of that explains the fact that Clytemnestra is now shacked up with the other assassin, Aegisthus. How is that supposed to avenge Iphigenia?
On top of that, Clytemnestra is a pretty rotten mother: she treats her daughter (Electra) horribly and hasn't been a mother at all to her son, Orestes.
In response to Clytemnestra's accusations that she is loud-mouthed and shameful, Electra simply replies: like mother like daughter.
Clytemnestra threatens that Electra will pay for her insolence once Aegisthus comes back. She then turns to the altar and proceeds to pray to Apollo. She hopes that the dream she had last night will not turn out to be an evil omen, and that she will continue to live her comfortable and happy life undisturbed. (Since this is a Greek tragedy, we know that her happy ending won't happen.)
Enter the old slave from the first scene with Orestes.
He asks if he has found King Aegisthus's palace, and then addresses Queen Clytemnestra.
The slave explains that he is a messenger sent from Phocis with an important message: Orestes is dead.
Electra is more than distraught: she wonders what she can live for now.
The old slave proceeds to tell a big fish tale. For several pages of entirely made-up baloney, he describes in ridiculous detail Orestes's accidental death in a chariot race.
At the end of the story, Clytemnestra is overcome with grief. She's sad that Orestes had to die in order to preserve her own life. "Motherhood is a strange thing," she says, "No wrong can make you hate the child you've borne" (770-1).
Then again, she is happy that she can live free of fear: Orestes had been sending her regular "I'm going to kill you" threats since he learned to hold a pen.
Electra, on the other hand is still distraught and still angry. She prays to Nemesis to avenge her brother.
The old slave is ready to leave, but Clytemnestra insists that he come inside and celebrate with her. So much for feeling guilty. Reluctantly, the old slave agrees. Electra is left outside to continue praying for vengeance.
Electra, greatly pained, declares that she will never again set foot in the palace. She'll just hang out on the doorstep. She adds that they will probably kill her, and that's fine with her, as "Life can only be pain. Far better to die" (821-2).
The Chorus laments Electra for several pages, while Electra laments herself.