When the play begins, Creon has been sent by Oedipus to the oracle at Delphi to find out if anything can be done to stop a devastating plague that has been ravaging Thebes. When Creon returns, he tells Oedipus that he has received an answer from the oracle. Creon thinks it would be better if he tells Oedipus the news privately, but the king responds that it should be announced here and now so that the citizens of Thebes can hear the answer too.

Creon reveals that the people of Thebes are being punished by the gods for harboring a murderer. The oracle told Creon that the killer of the last King of Thebes, Laius, is in the city and must be expelled for the plague to come to an end. The oracle had told Creon many details about the murder of Laius. Apparently, the old king had been on his way to Delphi when he and all but one of his companions were attacked by bandits and killed. After hearing Creon's report, Oedipus expresses own shock that the Thebans have neglected to find Laius's killer and bring him to justice. Oedipus vows to find Laius's killer and save his people. The irony here is that it was Oedipus himself who killed Laius.