This is the story of house of Atreus.
Agammenon: Agammenon has just returned from war. His wife Clyesmenstra, plots to kill him to avenge his daughters infanticide by Agammemon. As well it is also revenge by the gods for Agammenons willingness to make this scarifice and leading so many greeks and Trojans to their death in a meaningless war although the gods did not instruct C. to do this. As well A. brings back Cassandara his slave concubine who is cursed to see the future but never to be believed by Apollo. She forsees here own death and those of Agammenon and his troops.
Libatiion Bearers:
In this plays the Apollo sends Orestes to avenge his fathers death which the gods did not sanction. He does so and is attacked by the furies for matericide.
The Furies:
Athena passes judgement on Orestes because even though matercide is a crime it was sanctioned by a god to avenge a king. AS well the furies must be satisfied in there blood lust even if Oresties is found innocent.
The setting for the play is in the most primative of times which allows Aeschylus to create characters who do not follow the mores of his day more believeable. This play may have been the model for Hamlet.
Even after reading 100s of plays since the orestia this is still the most gripping drama that I have read. These plays and Hamelet are my favorites