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
Dionysus swears punishment.
Dionysus fills us in on all we need to know at the beginning of the play. The god comes out and launches into a monologue that gives us some exposition (back-story) about his bizarre birth. He then proceeds to let us know that he intends to punish all the folks in Thebes who say he's not a god. The first on his list are his mother's relatives, members of the house of Cadmus, the ruling family of Thebes. The stage is set for mortals to feel some godly wrath.
Conflict
Dionysus toys with Pentheus.
Pentheus shows up super angry, because all the women of Thebes, including his own mother, are out in the woods doing crazy rituals in honor of Dionysus. He arrests the Stranger, a guy he thinks is the leader of the Dionysian cult. Unfortunately for Pentheus, the Stranger is really Dionysus in disguise. The conflict gets revved up when Dionysus summons lightning and an earthquake to warn Pentheus against his blasphemy.
Complication
Dionysus convinces Pentheus to spy on the Maenads.
The conflict between Dionysus and Pentheus takes an interesting turn when Dionysus convinces the King to go spy on the rituals of the Maenads. The best part is that the straight laced Pentheus must do this while wearing women's clothes.
Climax
Pentheus is violently dismembered by his own mother.
The play reaches a grisly peak with the death of King Pentheus. A Messenger tells us all about how Agave, Pentheus's mother, ripped her son's body apart with her bare hands while he was spying on the Maenads.
Suspense
Agave returns bearing Pentheus's head.
Agave marches back to Thebes bearing the bloody head of Pentheus. The Dionysus-enchanted woman is under the impression that it's a lion's head she's carrying. There's all kinds of suspense as the audience watches Agave slowly come to her senses. It's horrific when she figures out she's really holding the head of her son.
Denouement
Dionysus sentences Cadmus and Agave.
Things begin to wind down as Dionysus appears and deals out punishments, banishing Agave and cursing Cadmus.
Conclusion
Dionysus is triumphant.
The play wraps up with Cadmus and Agave walking off to their fates. Dionysus hovers above, reveling in his godly glory.