The Sibyl tells the story of a certain Pythia, or high priestess, a chosen Greek virgin through whom Apollo, the god of light (and darkness), spoke when she entered into an ecstatic state in the dark and smoking holy of holies beneath the Temple of Apollo at Delphi. The priests' interpretations of her divinely inspired utterances constituted the Oracles of Delphi, among the most famous of the ancient world.

In her advanced age, the Sibyl is living with her mute son in a tiny hovel in the mountains far above Delphi when the wandering Jew comes to inquire about his fate. The wandering Jew had a happy life until, one day, a condemned criminal in his native town was passing by on his way to his execution. The wandering Jew had denied the condemned man the right to rest his head on the wall of his house and thus was cursed to never again find rest in this world and to never die. The wandering Jew later finds out that some believe that the condemned man was the son of god. He wonders how god (spelled with a lower-case "g" in The Sibyl) could be so cruel. He simply didn't wish to attract any negative attention from the authorities and certainly had no idea he was dealing with the son of god.

The Sibyl responds by telling her life story. She was a peasant girl from a simple but devout rural family, raised away from the corruptions of human life in Delphi, a town dependent on income from the pilgrims to the Temple of Apollo. She had always been different from others and attracted to the divine.

When she is called to be the new Pythias, she is greatly honored. She is a natural and the priesthood and the god are greatly pleased with her. The Townspeople are afraid of her, and her life as an outsider is reinforced by her service to the god. When he inhabits her, it is overwhelming, frightening, and powerful, rather than satisfying or comforting, as she had hoped. She does not get the feeling of safety she is seeking from the experience.

The Sibyl in the offseason falls in love with a one-armed former soldier and experiences human love for the first time. Her passion, combined with her desire for safety, in the end, spoils their love, as she becomes too attached to him. Eventually, he draws back, though he still cares for her. The Sibyl returns to temple service, where her crime of love is eventually found out. The god exacts his revenge on her lover, who is found dead in the river by which they first consummated their love. His bloodless body is grasping a laurel branch, the tree sacred to the god. In the holy of holies, she is again ravaged by the god but in a particularly fierce and frightening manner. The Townspeople seek to stone her for her earthly love, and she is driven from the temple precinct, but not before her truest friend from the temple saves her life. Standing in the light of the magnificent inner colonnades of the upper temple, the Sibyl feels safety and the protection of the god of light as she has always desired to feel it.

This gives her the inner strength to defy the mob and leave by the sacred road for her exile in the mountains, where, in a thunderstorm, she gives birth to a child, attended by wild goats that have led her to a mountain cave. She later figures out that her mute child could not have...