As Sophocles's Oedipus Rex opens, the city of Thebes is wracked by a plague that has led to a host of ills: the crops are blighted, the livestock barren, and the death toll mounts by the day. Tormented by the suffering of his people, King Oedipus dispatches his brother-in-law, Creon, to seek an answer to the city's terrible quandary from the Oracle of Delphi. The priestess tells him that the pollution of the city will only be cleansed when the murderer of Laius, the city's former ruler, is found and the king's death avenged.

As an impatient Oedipus questions Creon about the death of Laius, in lines 119–133 of the prologue, the latter man tells as much as he knows, explaining why the killers were never originally brought to justice:

Oedipus: And was there no one, no witness, no companion, to tell what happened?
Creon: They were all killed but one, and he got away, so frightened that he could remember one thing only.
Oedipus: What was that one thing? One may be the key to everything, if we resolve to use it.
Creon: He said that a band of highwaymen attacked them, outnumbered them, and overwhelmed the king.
Oedipus: Strange, that a highwayman should be so daring -- unless some faction here bribed him to do it.
Creon: We thought of that. But after Laius' death, new troubles arose and we had no avenger.
Oedipus: What troubles could prevent your hunting down the killers?
Creon: The riddling Sphinx's song made us deaf to all mysteries but her own.

Creon makes clear that the Thebans were mesmerized by the superior powers of the Sphinx, from whose destructive presence Oedipus had once freed the city. Only now, in the monster's absence, does he have the dreaded power to save it once again.