Bacchae is an anomaly among plays performed at the City Dionysia because it portrays the god himself. Athenians would have known that Dionysos was the son of Zeus by the mortal Semele and that he was a different sort of god in that he had experienced death and in that he apparently travelled widely in foreign parts and lived in the world rather than on Mount Olympus. It must have seemed strange, then, when the play began with Dionysos entering to introduce himself and to explain why he had decided to come to Thebes, which is where the events of the play will take place. Thebes, it seems, has refused to officially accept him for the god he is. He tells how Zeus had become enamored of Semele, the daughter of King Cadmus, the founder of Thebes. Disguised, he visited her often and eventually she became pregnant. The jealous Hera convinced Semele to ask Zeus to appear to her as himself. Having promised Semele to do anything she wished him to do, Zeus had no choice but to appear in his true thunderbolt form, which caused Semele’s death. Hermes rescued the unborn child, however, and Zeus hid it from Hera by sewing it into his thigh. Later, then, Dionysos was born of Zeus. Dionysos has come to Thebes not only on his own behalf, but to make the Thebans believe Semele’s original claim that she had been made pregnant by Zeus.

The middle of the play—the agon—involves the conflict between the protagonist Dionysos and the antagonist King Pentheus, representing Thebes. Pentheus, the unbeliever, enters and scolds two familiar mythological figures of Thebes, Cadmus and Tire-sias, who as old men, have become interested in the Dionysian rites practiced on Mount Cithaeron by Theban women, including the king’s own mother Agave, daughter of Cadmus. The two old men are dressed in the clothes of the Maenads (Bacchantes), the followers of Dionysos and participants in the Bacchanals, the Dionysian mysteries.

Pentheus announces that any Thebans participating in these mysteries will be arrested. The guards bring in the blond stranger, Dionysos, disguised as a priest of the rites. Pentheus, who has begun to come under the same Dionysian spell that has affected Cadmus and Tiresias, and the women of Thebes, questions the stranger about the rites, but the stranger will tell him nothing and is arrested. But Dionysos simply breaks out of prison and punishes Pentheus by causing an earthquake to destroy his palace.

A shepherd arrives to announce that Dionysian rites are taking place on Cithaeron and that the women are tearing apart cows in their ecstatic frenzy. In spite of himself, Pentheus is curious. The blond stranger, Dionysos, dresses the king in women’s clothes to disguise him, and Pentheus, now under the god’s spell, heads off for the mountain seeing strange visions of Thebes and bulls—the latter being common symbols of Dionysos.

The end or resolution of the play comes when it is reported by a messenger that Dionysos had placed Pentheus in his women’s clothes at the top of a tree so that he could watch the revelers. The god had then called his followers to witness the intruder. Led by Pentheus’ own mother, they had torn him to pieces, making him a de facto sacrifice to Dionysos.

It should be noted that Dionysos himself had suffered dismemberment in the Orphic tradition.