King Oedipus has a complex. Um—wait. We mean he has a problem.
Aware that a terrible curse has befallen Thebes, he sends his brother-in-law, Creon, to seek the advice of Apollo. Creon informs Oedipus that the curse will be lifted if the murderer of Laius—the former king—is found and prosecuted. Laius was murdered many years ago at a crossroads.
Oedipus dedicates himself to the discovery and prosecution of Laius’s murderer. Oedipus subjects a series of unwilling citizens to questioning, including a blind prophet. Teiresias, the blind prophet, informs Oedipus that Oedipus himself killed Laius. This news really bothers Oedipus, but his wife Jocasta tells him not to believe in prophets—they've been wrong before.
As an example, she tells Oedipus about how she and King Laius had a son who was prophesied to kill Laius and sleep with her. Well, she and Laius had the child killed, so obviously that prophecy didn't come true, right?
Jocasta's story doesn't comfort Oedipus. As a child, an old man told Oedipus that he was adopted, and that he would eventually kill his biological father and sleep with his biological mother. Not to mention, Oedipus once killed a man at a crossroads... which sounds a lot like the way Laius died.
Jocasta urges Oedipus not to look into the past any further, but he stubbornly ignores her. Oedipus goes on to question a messenger and a shepherd, both of whom have information about how Oedipus was abandoned as an infant and adopted by a new family. In a moment of insight, Jocasta realizes that she is Oedipus’s mother and that Laius was his father. Horrified at what has happened, she kills herself. Shortly thereafter, Oedipus, too, realizes that he was Laius’s murderer and that he’s been married to (and having children with) his mother. In horror and despair, he gouges his eyes out and is exiled from Thebes.
Fun times, eh?