After the capture of Troy, Cassandra, the daughter of the defeated and murdered King Priam, fell to Agamemnon's lot as a prize of war. Agamemnon brought her home with him to Mycenae as his concubine, further enraging Clytemnestra after the sacrifice of her daughter Iphegenia.

Clytemnestra was the twin/half-sister of Helen, over whom the war had been fought. To gain possession of Clytemnestra, Agamemon had killed her first husband and their children.

Initially faithful to her husband, during his 10 year absence, Aegisthus fell in love with her, and she eventually yielded to him. Upon the return of her husband, a great feast was given, during which Aegisthus and Clytemnestra. murdered both Agamemnon and Cassandra.