Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Tragic, Sympathetic, Foreboding, Ironic
It’s important to know Sophocles didn’t make the whole Oedipus story up. The Oedipus myth had been around, so Sophocles’s audience would have been familiar with the tragic ending before the play began. This has a distinct impact on the tone of the plays.
The actions of the characters (think of Oedipus’s endless determination to solve the mystery of Laius’s murder) take on a sense of irony and foreboding in this context:
OEDIPUS Let the storm burst, my fixed resolve still holds, To learn my lineage, be it ne'er so low. It may be she with all a woman's pride Thinks scorn of my base parentage. But I Who rank myself as Fortune's favorite child, The giver of good gifts, shall not be shamed. She is my mother and the changing moons My brethren, and with them I wax and wane. Thus sprung why should I fear to trace my birth? Nothing can make me other than I am. (1077-1086)
This little passage probably made ancient Greek audiences squirm with anxiety or shout out, "Stop being so determined, Oed! You're doomed!"
Because this play doesn't have a narrator, the tone is also profoundly shaped by the commentary of the Chorus. The Chorus expresses genuine sympathy for the situations of the characters, yet at the same time is acutely aware of the upcoming events.