What made Amy Stewart leave garden bestsellers behind for the novel ‘Girl Waits with Gun’?

On her last book tour, Amy Stewart served specialty cocktails at her readings. It was only fitting for her book, “The Drunken Botanist,” a historical tour of boozy plants. That was Stewart’s fifth work of nonfiction; since 2001 she’s been hitting bestseller lists with her quirky tales of the natural world with books that include “Wicked Plants” and “Flower Confidential.”

“We had so much fun,” she says of that tour. But it was something of a farewell — for now, she’s leaving nonfiction and gardens behind for an unexpected jaunt through Paterson, N.J., circa 1915.

Stewart had become obsessed with the long-forgotten tale of the real-life Kopp sisters. A century ago, when women hadn’t earned the right to vote, Constance, Norma and Fleurette stood up to one of the city’s wealthiest men and his violent gang of thugs.

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“I felt this very powerful sense of obligation,” Stewart says. “Everyone forgot about them, and I found them. I dug them up. I resurrected this story, and I can’t not tell it now.”

The Kopps are the stars of Stewart’s new zippy, winsome novel, “Girl Waits With Gun” (Houghton Mifflin Harcourt: 416 pp., $27). Filled with historical detail without being weighed down by it, the novel is a cinematic story of the women, the siege instigated by their powerful enemy, and their brave efforts in the face of real violence.

To fill in the gaps, Stewart wanted the tools available to a novelist; the book is told from Constance’s point of view. She’s the eldest, tall and solid — think “Game of Thrones’” Amazonian Brienne of Tarth minus armor and sword. After their mother’s death, it falls to Constance to preserve the family farm. Her sister Norma is capable and dour, a strong agrarian with a flock of carrier pigeons. Fleurette, the youngest, is a petite proto-flapper who would be flirty if only her sisters let her get into town once in a while.

But taking a trip into town is exactly what caused them to cross paths with the local factory owner, and then their troubles began. Using the threat of the notorious Black Hand, his thugs stake out their house, break windows, shoot at the sisters and threaten to kidnap Fleurette and sell her into slavery. Unlike most who’d suffered similarly, the Kopps allied with authorities to try to prosecute them. The book’s title comes from a headline about Constance, who showed up to meet extortionists not with the promised cash but with a handgun.

“What I wanted was for other people to have the same emotion I had when I found them…” Stewart says, “that sense of fun and spirit and adventure.”

During the course of the book, Constance quickly picks up investigative skills. In a subplot, she pursues a missing child, largely by following her instincts and understanding situations that men might not. That part of the story was invented by Stewart, but most of it is based on real events.

When she was working on the book, Stewart went to Paterson and found much of the 1915 scenery remains. “I stood in the creek where Fleurette got shot at. I have stood on the street corners, and I’ve been inside the jail,” she says.

Stewart lives in Humbolt County, so far north in California that in late August, when we spoke by Skype, she was already wearing a fleece pullover against the cold. There, she, her husband and business partners own Eureka Books, a bookstore in a Victorian-era storefront. Back then, the store sold accessories for horses and carriages like wheels, whips and tackle.

“We have a picture of when it was a buggy shop; there was this big old fake horse that they would wheel out into the street every day. A little ironic, when you consider that it was replaced by cars, and here we are, a bookstore,” she says, acknowledging that brick-and-mortar bookstores are considered an outdated throwback. “But we’re hanging on and doing good.”

Stewart had always loved writing, but in college at University of Texas at Austin she found herself studying anthropology and then getting a graduate degree there in community and regional planning. She moved to Santa Cruz and was working as an analyst and grant writer in the public sector when she penned her first book, the memoir “From the Ground Up: The Story of a First Garden.” It put her on a certain kind of nonfiction publishing path — and 14 years later, she’s stepping away from it, with plans to keep going.

What Stewart is working on now is another novel with Constance at its center. “I’m 46, and I think all writers at some point in their lives start to say, ‘How many more books do I get to write?’” she says. “Fiction is what I read. What I really want is to write the exact book that I want to read.”

But old habits die hard. On tour for this book — Stewart reads at Vroman’s on Sept. 28 — she’ll be serving up the New Jersey Automobile, a cocktail she adapted from a 1910s recipe in honor of the Kopp women.

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