Orestes and Pylades (both now disguised) reenter. As Orestes predicted, Aegisthus makes the two knock three times at his gates before being allowed in (a grave insult to a guest). At last a Porter enters to let them in, and Orestes asserts that he has vital news to tell the lord and lady of the house.
Aegisthus’ lack of hospitality, while it might seem trivial to modern readers, is a grave sin. The Greeks considered the guest/host relationship to be sacred, and had specific laws codifying the way that one behaved towards guests.
Clytemnestra enters, attended by Electra, and offers Pylades and Orestes a place to stay for the night, adding, “the eyes of Justice look on all we do.” Orestes tells her that he comes from Delphi, but that he has heard from a stranger that Clytemnestra’s son (Orestes himself) has died. Clytemnestra responds with (apparent) grief, saying that the news has “destroy[ed]” her. She blames the curse of the house of Atreus, and Orestes apologizes for bringing her such terrible news. Clytemnestra asserts that she still welcomes him as a guest, and orders Electra to escort Orestes and his servants to their rooms, before resolving to tell Aegisthus the news. All exit.
The fact that it is Clytemnestra, not Aegisthus, who greets Orestes already speaks to the corrupt nature of the household. In Ancient Greek culture, it was the job of the man of the house to greet guests, not the woman. Clytemnestra mentions “the eyes of Justice” as if to explain why she is being hospitable, but she also betrays her own guilt and fears with this phrase—she knows her bloody deed has not escaped the attention of the gods. Clytemnestra’s rather limited response to the news of Orestes’ death also displays her lack of motherly feeling. Compare her brief show of grief to the violent mourning rituals of Electra and the Chorus for Agamemnon—who has been dead much longer.