The play unfolds all necessary actions in the span of approximately a single day's happenings in the royal palace of Thebes. However, within this single revolution of the sun Sophocles has brought to light the total life of king Oedipus since his birth.
The dramatist has made a subtly designed technique of flashback revelation for this purpose. The play begins with the search for the cause of the plague, but the investigations as well as a certain chance happening all lead the actions swiftly into the main concern of the king's birth and past actions. Once the king's curiosity about his past actions is triggered (by the queen's mention of Phokis), Oedipus begins more investigation about his own past; this leads to more findings and more curiosity about his birth (with the arrival of the Corinthian messenger); and he finally reaches to complete knowledge about his birth, his past, and his crimes, within the span of a single day. What has happened in the last half century is very skillfully uncovered during the course of the day's investigation and happenings. The plot of Oedipus Rex is designed in such a way that the drama moves forward in action but backwards in revelation. That technique is called the technique of retrospect. Besides, Sophocles has also made extensive use of dramatic irony as a part of his dramatic plot. The process of backward movement in terms of knowledge, each step taken by Oedipus, contributes to the discovery and at the same time shocks the audience.
The plot construction of the play is essentially based on the classical norms of the unity of time, place and action. The unity of time means that the play must not cover a course of time not more than a single day: in Oedipus Rex also the whole plot of the play unfolds in the course of just a single day. It is a belief of the classical dramatists that the course of too long a period would seem artificial and hence an obstacle in the life-likeness of a drama. To maintain this classical norm the present play focuses on the last part of Oedipus's life where the whole truth about his life gets credibly exposed in a single day. The unity of place means that the happenings in the plot of a play must be set in places not too far away from each other, so that they will be credible to the audience: the actions of Oedipus Rex happen in front of the palace of the king, Oedipus, except a small bits of actions which are supposed to happen inside the palace. The play is indeed made up of four scenes added with a prologue and an epilogue, but all these scenes take place only within the compound of the palace. The unity of action means that all the actions, incidents or happenings should be strictly related to the central thematic issue, here the problem of Oedipus's birth, fate and past actions. From the very opening, nothing but the impulse and need to discover the murderer drags the play forward.
The design of the plot of this play can be seen in very structural patterns of several kinds. First of all, the plot can be seen as designed according to standard classical norm: a prologue begins the drama by introducing the characters, situation and also revealing the past background; then the body of the drama that follows is a made of episodes (actions) in four scenes; these episodes are interspersed by one ode after each of them; and the drama ends with an exodus, or exit, which is also the resolution or denouement of the play.
The prologue shows us a group of people lying pleading in front of the palace of the mythical king Oedipus. When the king comes and asks what the matter is, the eldest, who is a priest, replies him. During this dialogue, we learn about the present condition of the Thebans, the past of the glorious king Oedipus, who had solved the riddle of the Sphinx and saved them from misery. This exposition also very well highlights the character of Oedipus as a good and a great king, who is losing his sleep over the problem of the plague in the city. Finally, this preliminary scene also establishes the atmosphere and mood of the tragedy. Like the first act of modern dramas, this scene introduces the basic problem: the inciting event here is the message brought by Kreon that there is the murderer of the old king Laios and that the 'defilement' who should be removed from the country. This gives a decisive push to the action of the drama, a powerful motive to the actions of Oedipus, and a dramatic tension in the minds of the audience.
The prologue is followed by an ode; but the first ode is called the ‘parodos' or the 'entry' in the manner of a stately marching by the chorus, just like the first scene is called 'prologue' instead of ‘Scene I'. If the first scene (prologue) is the entry of the characters, the first ode (parodos) is the entry of the chorus. This was a ritual formula still common in Sophocles' time. In the first ode, the chorus sings about the misery of the Thebans and the necessity and greatness of the gods. They pray and make us feel the intensity of their grief, as the representative citizens of the city.
The first Scene (episode) develops the conflict. No sooner than the king has declared his intentions to punish the culprit, he is faced with the unexpected information that he is himself the evil person that he is seeking! Thinking that the old clairvoyant has been used by Kreon, Oedipus simply dismisses him and accuses Kreon. Thus the conflict branches out and intensifies. But the audience, as well as the chorus, becomes suspicious as to whether Oedipus is -himself the sinner in any way as yet unknown to him. In fact, the Greek audience used to know the story in advance, and they used to explore the theme of the drama in the unique way that the particular dramatist had focused. To this intensified dramatic situation, the chorus adds with yet another emphasis on the importance of the Delphic gods of prophecy. We are shocked. Though the chorus, in their second appearance (first ode) says that "these words (of Teiresias) are lies" for they think they were spoken in anger or out of the conspiracy, they have not lost, and will never lose, their faith in the gods of Delphi.
The second episode begins with the previous conflict between Oedipus and Kreon, which has now become public, but it quickly leads us into the second unexpected information from the queen. When the queen gives Oedipus an example of how false the oracles can be, namely the story of her son who was thrown in the forest, she happens to mention that her previous husband was killed at a place named "Phokis", instead of being killed by their own ill-fated child which they threw. This mention of the place of Laios's murder shocks Oedipus, and he begins to believe the blind Teiresias. Now the plot further develops with more rapidity; they send for the shepherd who had seen the murder of Laios. This episode is appropriately followed by second ode in which the chorus again emphasizes the frailty of man before the gods, as well as the inevitability of the rule of fate and the gods. They also add that "the tyrant is the child of Pride... (and) will be caught up in the net of pain", signaling that Oedipus is the son of pride and the fated tyrant!
The third scene begins by showing that proud Oedipus has been humbled; but again another piece of unexpected information shocks him. Instead of the shepherd, a messenger from Corinth arrives to tell him that Polybos is dead. But before Oedipus the time to shout in happiness, he is told that Polybos was not his father! This brings still another branch to the plot, at least in the eyes of Oedipus; but we soon find that Oedipus is gathering relevant detail for his investigation about the murderer of Laios! At this point, Oedipus gets the feeling that he has killed Laios, and so he might have to leave his dear Thebes and Thebans; he doesn't know the rest of the story. Irony builds up as in no other drama. The scene is again followed by the chorus lyrically expressing the wish that we knew the future. They would also like Oedipus to be the son of the gods. But alas, this is not so.
The fourth act brings about the crisis most dramatically and abruptly. The drama now comes to a close with yet another arrival of the most terrible truth; the information brought by the old shepherd tells Oedipus how he has been running into the very ditch of misery which he has consciously been trying to avoid. The discovery and the reversal of events take place at the same time. The resolution follows in the next scene. Along with the change in the destiny of the main characters and the realization of the inevitable as inevitable, the chorus now chants a song of resignation, an acceptance of man's frailty and the domination of fate.
In its typical classical pattern, the drama ends with the exodus, or the exit of the characters and the chorus. Oedipus is brought out after his offstage act of blinding himself on seeing the queen's dead body, and then he panics in the most heart-rending manner. He laments for all his past and his ill-fated life, and he also moans for the destiny of his children. But his mind is full of conflicts of several kinds. Kreon takes over and commands that he be taken inside, for the moment, before being driven away from the city. The drama ends with an emphatic thematic speech by the oldest member of the chorus, the choragos, who tells the audience not to presume about life before the moment of death.
In conclusion, the plot of Oedipus Rex is perfect; nothing is left loose or illogical. The unities are maintained and the actions and dialogue are fully convincing. There is poetic justice and there are all reasons for the audience's satisfaction and emotional/ intellectual participation. The process of unfolding the truth of the life and destiny of Oedipus also changes and enlightens the audience to realize their own human condition.