For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Agamemnon is coming back after ten years' exile.
Act II
Agamemnon arrives home with the Trojan princess Cassandra. His wife, Clytemnestra, welcomes them in, but Cassandra prophesies that they are about to be killed.
Act III
Clytemnestra kills Agamemnon. She is helped by her new lover, Aegisthus, Agamemnon's nephew, whose siblings were murdered by Agamemnon's father, Atreus.