Dionysus, Greek god of wine, fertility, ritual madness, and ecstasy returns to his hometown of Thebes, having sent the women of Asia wild with his religion. He explains that he’s here to avenge his mother, Semele, who he feels was wronged by her sisters and is being disrespected by the current king of Thebes, Dionysus’ cousin Pentheus. Dionysus tells his backstory: Semele’s lover was Zeus, king of the gods, and their relationship made Zeus’ wife, Hera, jealous. She tricked Semele into asking Zeus to reveal himself in his true form, a dangerous lightning storm that fatally struck Semele. Zeus then stitched Dionysus, his unborn son, into his thigh for protection. Dionysus is angry that Semele’s sisters and Pentheus cast doubt on this story, suggesting it was invented by Cadmus, the sisters’ father and Dionysus and Pentheus’ grandfather, in order to save face over Semele’s embarrassing affair with a mortal. Accordingly, Dionysus wants to exact revenge and prove his godliness in doing so.
Dionysus is accompanied by a band of his hedonistic female followers, the Bacchae, and has converted the Theban women into Bacchae too, including his aunts, Ino, Autonoe, and Agave, Pentheus’ mother. These new converts are up on Mount Cithaeron, indulging in Dionysian rituals of drunkenness and sexual liberation. Meanwhile, Dionysus has cunningly taken on human form, disguised as a priest of his own religion.
Cadmus, the previous ruler of Thebes, and Tiresias, an elderly blind prophet, want to pay tribute to Dionysus, and dress up in fawn-skin and carry thyrsi, tall rods wrapped in ivy and topped with pine cones. At this moment, Pentheus arrives back in Thebes, having been out of the country for a few days. He openly scorns Dionysus, doubting his godliness, and ridicules Cadmus and Tiresias for wanting to worship him. He promises to put an end to the Dionysian priest’s fraudulent magic, vowing to imprison and behead him. The two old men warn Pentheus that he risks bringing tragedy upon himself by disobeying a god.
Pentheus orders his guards to capture the priest (Dionysus in disguise), who gives himself up willingly. The king interrogates his prisoner, evidently intrigued by his attractive physical appearance, before becoming frustrated at Dionysus’ evasiveness. Pentheus cuts off Dionysus’ hair and snatches his thyrsus from him, and instructs his guards to imprison Dionysus in the palace. The chorus (a group of Bacchae that functions as a commentary to the play’s events) calls for Dionysus, who uses his powers to create an earthquake and fire that quickly bring the palace crashing down. Dionysus explains to the chorus that Pentheus hadn’t actually imprisoned him, but a bull, and that the king had tried to stab him, but instead just thrusted pointlessly at the shadows.
Pentheus exits the palace, only to see Dionysus (still disguised as the priest) bafflingly standing right in front of him. A herdsman arrives, recounting a terrible tale of the Bacchae on the mountain. He says he saw the Bacchae, led by Agave, Ino, and Autonoe, relaxing among the fir trees, using their thyrsi to draw milk, wine, and honey from the ground. Not only that, but the women seemed to be nursing wild animals at their breasts. Seeing this, the herdsman had thought to help the king by ensnaring Agave and bringing her back to the palace. However, the Bacchae spotted the herdsman and his accomplices and quickly turned on them; when the men escaped, the women then turned on some nearby cattle and tore them apart limb from limb. Still enraged, the Bacchae swooped on nearby villages, snatching children and pillaging houses. When the villagers fought back, the Bacchae’s thyrsi ripped open their flesh. The herdsman ends his tale by warning Pentheus that, “whoever this god may be,” he is clearly so powerful that he ought to be welcomed to Thebes.
Pentheus is evidently intrigued by the herdsman’s tale; Dionysus (as the priest) plays on this by asking Pentheus if he would like the chance to spy on the Bacchae and observe their frightening behavior up close. Surprisingly, the king is desperate to do so; Dionysus tells him that the best way is for Pentheus to dress as a woman so that the Bacchae won’t attack him like they did the herdsman. Pentheus agrees to cross-dress and goes into the palace ruins to put on his outfit, which Dionysus helps him with. When they return, Pentheus clearly revels in his new identity, asking Dionysus how he looks as a woman and wanting to make sure every part of the outfit is just right. As they head towards the mountain together, the chorus calls on the “swift hounds of madness” to bring about Pentheus’ death.
The second messenger appears on stage, bringing terrible news of Pentheus’ death. He recounts how Dionysus bent down the trunk of a tall fir tree and sat Pentheus atop it so the King could get a better view of the Bacchae. Once Pentheus was trapped on the top of the tree, Dionysus called out to his followers from the sky to attack the mortal who “mocked” him; Pentheus, like the cattle earlier, was literally torn apart in a gory and brutal attack led by his own mother, who failed to recognize him despite his desperate attempts to reveal his true identity.
Back at the palace, the chorus sings the praises of Pentheus’ gruesome death. Agave returns, parading Pentheus’ head on top her thyrsus. She thinks she has killed a mountain lion and boasts to Cadmus, her father, of her hunting prowess. He beckons her to stare at the sky, which seems to shake the madness from her mind. She looks at the Pentheus’ head and realizes her terrible mistake, though she remembers nothing of the murder. Dionysus appears, taunting Agave and Cadmus and admonishing them for not worshipping him as he feels he deserves. He then delivers Cadmus’ fate: the old man and his wife, Harmonia, are to be turned into snakes and destined to return to Greece as barbarian invaders (though eventually they’ll be brought to the “Land of the Blessed”). Dionysus leaves, and Cadmus and Agave bid a tragic farewell to one another. They exit the stage in opposite directions, signaling the destruction of their royal household. The chorus has the last word, telling the audience that gods behave in unexpected ways, “and that is what has happened here today.”