As Jocasta makes a sacrifice to Apollo, a messenger arrives to announce the death of Polybus. Oedipus rejoices at the news that the father he feared he would kill has died of natural causes, but he continues to worry about the prophecy because his mother still lives.
Overhearing Oedipus, the messenger tells the king that he has nothing to worry about, since Polybus and Merope were not his real parents. This news stuns Oedipus, and he awaits the shepherd to learn the truth of his birth.
Jocasta now realizes that Oedipus is the baby she and Laius abandoned, and that the prophecy has come true. She begs Oedipus to stop his inquiry, but he refuses, and she runs into the palace screaming.
This scene turns on multiple ironies as Oedipus draws closer to the revelation of his birth. For example, the messenger from Corinth brings conflicting news — your father is dead, he tells Oedipus, but he is not your father.
Even the opening ritual of the episode involves irony. Despite her earlier skepticism, Jocasta burns incense to Apollo. Ironically, she implores Apollo — the source of this prophetic truth and the god of prophecy — to release Oedipus from his fears about the very prophecy Apollo himself has given.
Yet the news from the messenger returns Jocasta to her original views on prophecy. She even brushes aside Oedipus' continuing anxiety about his mother with the impious suggestion that he "live at random" (1072), completely oblivious to Apollo's warning. Her bravado is shattered, however, as the scene unfolds and she realizes that Oedipus is, in fact, the child she abandoned.
Meanwhile, Apollo seems to have answered Jocasta's prayer. With the terrible truth pressing in on him, Oedipus calls triumphantly for the shepherd who will tell him everything. At this moment, Oedipus revels in the kind of pride that always precedes the downfall of a tragic hero. He seems proud even in his (mistaken) belief that he is the son of a shepherd and the goddess Chance, "the giver of all good things" (1189). In calling Chance a goddess, Oedipus follows Jocasta's questionable advice to acknowledge that "chance rules our lives" (1070).
By now, the truth of Oedipus' birth is practically unavoidable, but the fact that he still cannot guess it — and that Jocasta has only now realized it — would not have seemed strange to Sophocles' audience. Sophocles means for the audience to suspend their disbelief, and let the tragedy unfold according to its own conventions.