 However, in terms of the chronology of events that the plays describe, it comes first, followed by "Oedipus at Colonus" and then "Antigone".Prior to the start of "Oedipus Rex", Oedipus has become the king of Thebes while unwittingly fulfilling a prophecy that he would kill his father, Laius (the previous king), and marry his mother, Jocasta (whom Oedipus took as his queen after solving the riddle of the Sphinx).The action of Sophocles's play concerns Oedipus's search for the murderer of Laius in order to end a plague ravaging Thebes, unaware that the killer he is looking for is none other than himself.