Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
George and Martha are trapped in a bitter world of illusion.
We begin with two people who have been trying to tear each other down for years. They hide behind illusions – like their imaginary son – to make it through the bitterness that is their lives.
Conflict
Nick and Honey arrive. The shattering of illusions begins.
George and Martha drag their young guests into their verbal warfare. As the battle of wills rages, illusions begin to crack. Social niceties soon fall by the wayside and the characters' ugliness is on full display.
Complication
Martha attempts to sleep with Nick.
When Martha goes upstairs with Nick it's the really the last straw for George. Though he acts like he doesn't care, it drives him toward his climactic action.
Climax
The Exorcism.
After the loss of many battles, George finally wins his war with Martha. When he "kills" their imaginary son and exposes him as an illusion, his wife's will to fight finally seems broken.
Suspense
N/A
There's no time for more suspense as the play immediately begins heading into its falling action.
Denouement
The guests leave; Martha begs.
The play draws to a close as Nick and Honey take their leave. Martha makes one last effort to convince George that they should "give birth" to their son again. He refuses.
Conclusion
George and Martha begin to live with no illusions.
At the play's final moment George and Martha are left alone together, stripped of all illusions. They have nothing but the cold hard reality of their existence to comfort them. In a strange way, they seem to be closer to each other than they've been for the entire play.