Versions of the Myth … Homer – In Homer’s account … Clytemnestra played a passive role in Agamemnon’s death, merely permitting her lover, Aegisthus, to murder Agamemnon… In this narrative, the driving force of Agamemnon’s death is Aegisthus’ desire to avenge his brothers and uncles, and take the throne which he believes belongs by right to his family.
Aeschylus – In the play Oresteia … Clytemnestra is the motivating force who plans to kill Agamemnon to avenge her murdered family members. She commits the killing herself, with a double-edged axe called a pelekus. Clytemnestra kills Agamemnon using the same method that would be used to sacrifice an animal to the gods: three blows, with a prayer to the gods uttered before striking the third. This is doubtless a reference to the sacrificial killing by Agamemnon of their daughter.
The Death of Clytemnestra … Aegisthus would remain as king for just seven years, for by that time Orestes was of age, and the son of Agamemnon and Clytemnestra returned to Mycenae to seek revenge upon the killers of his father. Aegisthus was thus killed by Orestes, as was his half-brother, Aletes, but it was also said that Orestes committed a great wrong when he killed his mother despite her pleadings and prayers. The killing of Clytemnestra would bring forth the wrath of the Erinyes upon Orestes, and indeed it was said that the very ghost of Clytemnestra cajoled the Erinyes in their persecution of her son. Eventually, Orestes was released from the hounding of the Erinyes when he was cleared of murder by Athena, and Orestes would subsequently marry his half-sister by Clytemnestra, Erigone.
… In short, yet another story of Happy Families.
Clytemnestra’s Story (PDF for download – 2 pages)