On a bright and breezy day, Pulitzer Prize-winning author and former foreign correspondent Geraldine Brooks wades into the garden outside the National Museum of the American Indian, investigating the buttercups and medicinal herbs.

“Oh, that seed would have been an important food source,” the Australian-born Brooks says, inspecting the grassy meadow. “Everything planted at this museum is important in Native American traditions.”

In her latest book, “Caleb’s Crossing,” Brooks unearths telling details of daily Native American life to build the world of Caleb Cheeshahteaumauk, who in 1665 was the first Native American to graduate from Harvard University.

Brooks weaves Caleb’s fictional story using as a jumping-off point the only artifact she knows of: a letter Caleb wrote in Latin to his English Christian benefactors, a document that has been translated and is studied by scholars of the period. In the letter, the young student refers to the myth of Orpheus, who was able to cross into other cultures, just as Caleb was able to cross into the world of Harvard.

Brooks describes this novel as a “love story in the broadest sense, but not the narrow, bodice-ripper one.”

She’s in Washington on book tour for “Caleb’s Crossing,” and she’s eager to eat lunch at the museum’s cafe, Mitsitam, which means “Let’s eat!” in the language of the Delaware and Piscataway Indians. Mitsitam is one of the most popular museum cafes in the city, with food stations drawing on tribal culinary traditions from five areas in the Americas.

Brooks picks a traditional meal from the Native American Northeastern Woodlands region — maple-brined turkey and a colorful plate of “Three Sisters Salad,” a toss of corn, beans and squash.

“Oh, that’s beautiful,” she says. “I did some research at this museum. But I never had time to eat.”

That’s not surprising, given Brooks’s famously meticulous research and drive to give authenticity to her storytelling. The historical novel is told through the voice of Bethia Mayfield, 12, the restless “girlchild” of a Puritan minister, growing up as a pioneer on Martha’s Vineyard, then inhabited by Caleb’s Wampanoag tribe.

“Storm Eyes,” as Caleb calls Bethia, is frustrated with her life of mending clothes and trying to control her daily impulse to break away from the hearth and explore the most beautiful hiding places on lush Martha’s Vineyard. Bethia and Caleb become secret soul mates, even as her father is determined to convert Caleb’s tribe to Christianity.

The idea for “Caleb’s Crossing” originated on a summer visit to the Vineyard around 2005. Brooks was looking at a map of the Wampanoag of Massachusetts, showing sites on the island of tribal significance. It noted the island as Caleb’s birthplace and named him as Harvard’s first Native American graduate.

“At first I thought it read he graduated in 1965. But it was 1665! I was blown off my perch,” says Brooks.

She realized that Caleb’s life would make a great subject for a book, so she started searching for documents or research about him. But so little was known, other than that letter, that Brooks wanted to fill the historical void by imagining his world.

“I talked with tribal members, read translations of early documents in the [Wampanoag people’s] Wopanaak language, then delved into the archives of Harvard and the Massachusetts Bay Colony,” she said. “I read the correspondence between colonial leaders and benefactors in England who donated funds for the education and conversion to Christianity of Indians in the 17th century.”

“Throughout the research, my dream was that this big stack of documents or a journal written by Caleb would emerge,” she said. “But it never did.”

Caleb wasn’t the only mystery character in her proposed tale. When she began her research— in 2006, while she was at Harvard as a Radcliffe fellow — she quickly realized there were no journals written by women from that period.

So Brooks read court records and private letters of women of the period to capture what Bethia’s cadence might have sounded like: “I forgot he was a half-naked, sassafras-scented heathen anointed with raccoon grease. He was, quite simply, my dearest friend,” Bethia says after meeting Caleb.

Brooks’s energy is the source of her rapid-fire production. “Caleb’s Crossing” is her fourth book in a decade.

“Brooks is as adventurous a novelist as she once was a journalist, reporting from the Balkans in the 1990s,” Jane Smiley wrote in a recent review of “Caleb’s Crossing” in the New York Times. Smiley wrote that the book “reconfirms Geraldine Brooks’s reputation as one of our most supple and insightful novelists.”

Before launching her book-writing career, Brooks was a foreign correspondent for the Wall Street Journal. She’s married to Tony Horwitz, a fellow Journal reporter and author, and they spent years reporting, together and independently, around the globe, chasing stories about coups and conflicts in Sudan and Somalia and uprisings in Kurdistan and the Balkans.

She developed an eye twitch from the stress of living out of suitcases and never knowing which war zone she was going to be in next.

“I loved the foreign correspondent life, and after a while I just thought that was the way I was, that’s the way life is,” she said.

Around 1992, after six years on the road, Brooks took a leave of absence to write “Nine Parts of Desire: The Hidden Life of Islamic Women,” which penetrates the hidden world of women in Saudi Arabia and Iran.

She returned to the field, but while reporting in 1994 on the uprising in the oil-rich Niger Delta, Ni­ger­ian authorities threw her in jail. While there, she made a deal with herself.

“I was 38 and decided that if I ever got out of the slammer, the first thing I would do was get pregnant,” she says.

When she got out of jail, she quit the paper. Her eye twitch disappeared.

Brooks and Horwitz now have two sons — Nathaniel, 15, and Bizuayehu, 8, who was adopted from Ethiopia. She grabs any chance to read them children’s stories, which she says helps her own writing.

“I love literature for kids because it has an actual plot,” she says. “It’s a real wake-up call when Point A leads to Point B!”

She lives on Martha’s Vineyard with the boys and Horwitz, who also has a Pulitzer Prize.

Because of her newspaper training, Brooks is a fairly disciplined writer, she says, “but that doesn’t mean I don’t find myself in a hot bath on a cold day, with a stack of New Yorkers.”

She finds her best stories in the unexplored tales that sit in front of us or “the absence in the room,” as she calls it. In her novel “March,” Brooks was inspired by the “wonderfully absent” father in “Little Women.”

She had just finished writing “March” when she took a deep breath and planned a day of beauty and personal attention. She spotted a traveling mammogram van and thought, “Great, I’m done writing. I’ll go get a leg wax and then a mammogram.”

The results showed breast cancer.

Brooks treated herself “very gently,” during two rounds of surgery, chemotherapy, radiation. In a moment of sheer triumph, the book won the Pulitzer.

“I was helping my son paint models of space aliens and I was dressed in a schmata [old dress] when I got the call,” she said. “A photographer came to the house and took a picture. My mom in Australia called after that photo appeared and said she hoped I would use the prize money to buy a decent frock.”

Soon afterward, she felt the drive to get busy living.

“I don’t procrastinate anymore,” she says, after finishing lunch. “I seize the moment.”

Like Caleb, Brooks has made her own crossing — from fast-paced reporting to the slower rhythms of a novelist. Yet she employs her reporting skills to inform her historical fiction.

“I think I’m still living off the fat of my reporting career. I love the deep dive into the research,” she says. And she enjoys life without an eye twitch.