Nimue recounts her origins: a fifteen-year-old laundress at Rutupiae, an old Roman fort, struggling to support her younger sister Mary after their parents died of typhoid. The castle steward pressured her into prostitution, and starvation loomed. Then the wizard Merlin arrived and assembled an elaborate armillary sphere in the great hall, holding nightly parties as if waiting for something.

One night, half-starved, Nimue snuck upstairs to steal food. The steward seized her, but Merlin intervened, and as Nimue approached his machine, it ignited and came to life, recognizing her as its destined operator. Merlin took her on as his apprentice, requiring her to send Mary away to a distant cousin and visit only once a year. Over three years he taught her spells and how to negotiate with Britain's lesser spirits, though she remained a devout Christian and never felt safe with him.

One morning Merlin summoned her and casually proposed treason: Arthur was a flawed, self-loathing king incapable of fathering an heir, so Merlin would impersonate him to impregnate Guinevere, then arrange Arthur's death and rule as regent. He then forcibly kissed Nimue, shifting through forms (Lancelot, Guinevere, Arthur), and threw extinct flower pollen in her face to make her pliant.

Nimue had prepared. Immune to the pollen, she cut off Merlin's amulets and spoke a marid's word that blasted him through the tower wall. A magical battle followed across Britain: Merlin grew giant, then became a black dragon; Nimue used favors from minor spirits (Tumbo the hill, the Slip river, Awel the wind) and transformed into a swift. She lured Merlin into the clouds, where Taranis the thunder god (whom Merlin had summoned) struck Merlin down instead of her, sending his mind into the dream realm.

Saved briefly by Durelas, the liminal god, who acted on behalf of small spirits Nimue had been kind to, she found herself swallowed by dream-Merlin. He revealed his shameful history: betraying his fellow druids at Ynys Môn to survive the Roman massacre, and his obsessive desire for her. Nimue then revealed that he was the one trapped in dreams while his body lay senseless. She flew back to his tower as a falling star (which Merlin had called down to bury her grave) crashed into his sleeping body, burying him deep. The tower became Nimue's, and Merlin's curse upon her was that no one would believe her account.