With the opening of the play "Oedipus Rex," famines, fires, and plagues have beset the town of Thebes. Oedipus asks the people why they pray and "lament" since they have come to petition him:
Tell me, and never doubt that I will help you/In every way I can; I should be heartless/Were I not moved to find you suppliant here.
Because Oedipus is revered for having solved the riddle of the Sphinx, the priest asks him to "Find us our safety, find us a remedy" to the troubles upon them. When Kreon, the brother of Jocaste, wife of Oedipus, enters, he tells Oedipus that the oracle reports that Apollo has commanded them
to expel from the land of Thebes/ An old defilement we are sheltering.
Kreon further explains that it was the murder of King Laios, who once ruled Thebes, that is the cause of th "plague-wind on the city." And, Apollo commands the people "To take revenge upon whoever killed him."
This last statement is an example of situational irony since Oedipus does not realize that it is he himself who has killed Laios. This irony is pivotal to the play and its role of fate as Oedipus feels that he exercises his freedom of choice as Oedipus investigates the cause of the murder only to finally realize his own fateful act, his tragic mistake, or harmatia, which has brought upon Thebes the curse of the "plague-wind."