At the start of the play, the city of Thebes is suffering terribly. Citizens are dying from plague, crops fail, women are dying in childbirth and their babies are stillborn. A group of priests comes to the royal palace to ask for help from Oedipus, their king who once saved them from the tyranny of the terrible Sphinx. Oedipus has already sent his brother-in-law, Creon, to the oracle of the god Apollo to find out what can be done. (A little background: before Oedipus arrived in Thebes, the previous king, Laius, was murdered under mysterious circumstances and the murderer was never found. When Oedipus arrived in Thebes and saved the city, he was made king and married the widowed queen, Jocasta, sister of Creon.) Now Creon returns with the oracle's news: for the plague to be lifted from the city, the murderer of Laius must be discovered and punished. The oracle claims that the murderer is still living in Thebes.
Oedipus curses the unknown murderer and swears he will find and punish him. He orders the people of Thebes, under punishment of exile, to give any information they have about the death of Laius. Oedipus sends for Tiresias, the blind prophet, to help with the investigation. Tiresias comes, but refuses to tell Oedipus what he has seen in his prophetic visions. Oedipus accuses Tiresias of playing a part in Laius's death. Tiresias grows angry and says that Oedipus is the cause of the plague—he is the murderer of Laius. As the argument escalates, Oedipus accuses Tiresias of plotting with Creon to overthrow him, while Tiresias hints at other terrible things that Oedipus has done.
Convinced that Creon is plotting to overthrow him, Oedipus declares his intention to banish or execute his brother-in-law. Jocasta and the chorus believe Creon is innocent and beg Oedipus to let Creon go. He relents, reluctantly, still convinced of Creon's guilt. Jocasta tells Oedipus not to put any stock in what prophets and seers say. As an example, she tells him the prophecy she once received—that Laius, her first husband, would be killed by their own son. And yet, Laius was killed by strangers, and her own infant son was left to die in the mountains. But her description of where Laius was killed—a triple-crossroad—worries Oedipus. It's the same place where Oedipus once fought with several people and killed them, one of whom fit the description of Laius. He asks that the surviving eyewitness to Laius's murder be brought to him. He tells Jocasta that oracles have played a big part in his life as well—he received a prophecy that he would kill his father and sleep with his mother, which is why he left Corinth, the city he was raised in, and never returned.
An old messenger arrives from Corinth with the news that Oedipus's father, King Polybus, has died of old age. This encourages Oedipus. It seems his prophecy might not come true, but he remains worried because his mother is still alive. The messenger tells him not to worry—the king and queen of Corinth were not his real parents. The messenger himself brought Oedipus as a baby to the royal family as a gift after a shepherd found the boy in the mountains and gave him to the messenger. The shepherd was the same man Oedipus has already sent for—the eyewitness to Laius's murder. Jocasta begs Oedipus to abandon his search for his origins, but Oedipus insists he must know the story of his birth. Jocasta cries out in agony and leaves the stage. The shepherd arrives but doesn't want to tell what he knows. Only under threat of death does he reveal that he disobeyed the order to kill the infant son of Laius and Jocasta, and instead gave that baby to the messenger. That baby was Oedipus, who in fact killed his father Laius and married his mother. Oedipus realizes that he has fulfilled his awful prophecy. Queen Jocasta kills herself and Oedipus, in a fit of grief, gouges out his own eyes. Blind and grief-stricken, Oedipus bemoans his fate. Creon, after consulting an oracle, grants Oedipus's request and banishes him from Thebes.
