Eumenides

The final play of the Oresteia, called The Eumenides (Εὐμενίδες, Eumenídes), illustrates how the sequence of events in the trilogy ends up in the development of social order or a proper judicial system in Athenian society. 
In this play, Orestes is hunted down and tormented by the Furies, a trio of goddesses known to be the instruments of justice, who are also referred to as the 'Gracious Ones' (Eumenides). They relentlessly pursue Orestes for the killing of his mother. However, through the intervention of Apollo, Orestes is able to escape them for a brief moment while they are asleep and head to Athens under the protection of Hermes. Seeing the Furies asleep, Clytemnestra's ghost comes to wake them up to obtain justice on her son Orestes for killing her.