Electra comes arrives at Agamemnon's tomb and makes a speech revealing that it was Clytemnestra who sent her and the slave-women to make the offerings.
Electra feels awkward because she doesn't know what she can say to her father's spirit on Clytemnestra's behalf; everything seems inappropriate, since it is coming from Agamemnon's murderer. She asks the Chorus (i.e., the group of slave-women) for advice. After some back and forth, they tell her to pray that Orestes will come from abroad to avenge Agamemnon's death.
After Electra makes this prayer, she notices the locks of hair that Orestes left on the tomb. She can't think of anybody who would want to make such an offering other than her brother Orestes. Then she notices that the hair looks like her own hair, and the footprints around the tomb match her own as well!
Electra is half-convinced that Orestes has returned, but half-convinced that it's impossible that he came.
After Orestes reveals himself and his mission to avenge his father's death, he, Electra, and the Chorus join together in singing and chanting prayers to Agamemnon, asking for his help in getting revenge on Clytemnestra and Aegisthus.
Orestes takes charge of revenge plan: he tells Electra to go inside the palace and act natural. She obeys him.