NEW YORK — Louise Glück’s next book was as unexpected for her as it will likely be for the Nobel laureate’s readers.

After more than 10 poetry collections and two books of essays, including such prize winners as “The Wild Iris” and “Faithful and Virtuous Night,” the 79-year-old writer has completed her first prose narrative, to come out in October. “Marigold and Rose: A Fiction” runs 64 pages, unfolding like a fable as Glück imagines the thoughts of infant twins.

She has written about children before, notably in her acclaimed 1990 collection “Ararat.” But while her poems were drawn in part from her childhood and her experiences as a parent, “Marigold and Rose” originates in a very contemporary way: from videos of her granddaughters Emmy and Lizzy sent by her son from California while Glück was unable to visit because of the pandemic.

“I remember telling someone that watching twins was like going to the zoo; you see behavior you don’t ordinarily see in babies, because these children are having relationships with each other before they have relationships with almost anyone else,” Glück, who lives in Cambridge, Massachusetts, said during a recent telephone interview.

Watching the videos, she said, “became to me an obsession.”

The sounds and images of Emmy and Lizzy eventually led to words. Glück composed a short chapter and emailed it her son, who told her he liked the work so much he was reading it aloud to the family, even if the babies were too young to understand. She continued writing chapters and sending them, and within weeks had finished what became “Marigold and Rose.”

“It was just bliss to write,” says Glück, who wondered if the speed of the writing process might “unnerve and mystify” some readers. “People don’t like to hear that because it suggests shallowness. But in my experience some of my best work comes very fluently. I don’t see it as a bad thing. It usually means you’re riding a wave.”

From the opening lines — “Marigold was absorbed in her book; she had gotten as far as the V. Rose didn’t care for books” — Glück joins and contrasts the lives of the introspective Marigold and the sociable Rose. Marigold is already forming a story in her head, while looking upon the “calm self-confidence” of her twin and reasoning that “Together they included everything.”

In chapters with such titles as “Sharing with Bunnies” and “Rose and the Elephant,” Marigold and Rose spend a summer’s day watching their mother garden, Marigold comes up with a title for her planned book (“The Childhood of Mother”), Rose begins speaking and the parents consider buying a house. Glück even places a version of herself in the story — as “Other Grandmother,” the one “not interested in the things babies were interested in.”

Glück, winner of the Nobel in 2020, explained in her prize lecture that she was drawn to poems that make readers or listeners the “recipient of a confidence or an outcry, sometimes as co-conspirator.” In “Marigold and Rose,” Glück has granted herself and her fans the knowledge that the narrator of her poem “Child Crying Out” longs for. Part of the “Ararat” collection, “Child Crying Out” is a meditation on the distance between people, including a mother’s lament over the silence of her son’s soul, the feeling he is “far away” even when she holds him in her arms.

“There’s much more anguish in that poem because the speaker is the mother and the child is unreachable in a certain way,” Glück says.

“I remember reading Dr. Spock at the time (when her son was an infant), about how a mother always knows the meaning of a child’s cry. And I thought, ‘Great, I flunked already.’ I was struggling. I had no idea. I couldn’t figure it out and I felt helpless and despondent and confused. It got easier. But it only got easier when he started to talk.”

Glück has never published a novel or story collection and says that before “Marigold and Rose” she had no desire to write narrative fiction. She remembers attempting a short story in her late teens and finding the result uninspiring — “sterile,” “just terrible.” Decades of letter writing and essays served to “oil” the mechanism for extended prose, she says, but she still didn’t expect to complete a work like her new one.

“I would have said the chances I would write a book in prose were zero,” she explained. “No chance in the world.”

Glück’s editor at Farrar, Straus & Giroux, Jonathan Galassi, says the new book was a “total surprise,” but also cites what he calls “quintessential Glück humor” — the wry touch of having Marigold be a writer before she can even read. Her friend and fellow author Kathryn Davis, to whom Glück sends early drafts of her work, said she wasn’t surprised, if only because Gluck is “astonishingly willing to admit change into her life.”

“The arrival of the twin girls … was prelude to the possibility of even bigger changes,” Davis told the AP. “The narrative arrived like the twins, like the recounting of a dream, uninterrupted, immutable.”

Glück refers half-jokingly to “Marigold and Rose” as “Portrait of the Artist as a Young Baby.” The tone is engaging and witty, but Glück weaves in larger and more primal themes, giving the book the feeling of a creation myth, an awakening from innocence. The twins’ maternal grandmother dies (“Grandmother went to heaven. This is not like when Father went to work”), and the babies discover that being “happy” can only be understood when they’re not. Marigold herself realizes that the accumulation, and arrangement, of words co-exist with loss and change.

“Everything will disappear. Still, she thought. I know more words now. She made a list in her head of all the words she knew: Mama, Dada, bear, bee, hat,” Glück writes.

“And both these things would continue happening: everything will disappear but I will know many words. More and more and more and more, and then I will write my book.”