The joy of writing is in the slow unraveling of secrets, says Erin Lindsay McCabe, whose debut historical novel I Shall Be Near to You follows Rosetta, a young newlywed who pretends to be a man so she can serve in the Civil War beside her husband Jeremiah.

The fiction of the book is based on the very real letters of Rosetta Wakeman, which McCabe discovered while looking for a topic for an undergrad history assignment at the University of California, Santa Cruz. A standard college essay followed, but the mystery of Rosetta and other women who covertly served in the Civil War stuck with the author for more than a decade.

“I’m very interested in the secrets people keep and why,” McCabe says. “That’s what I found so interesting about Rosetta and the other women. They didn’t have to do this. They chose to go into battle. For the women who went with family members, it required the people around them to keep secrets, too.”

The real-life Rosetta died after being hospitalized with dysentery, but was still buried as a man after serving in the Union army, McCabe says, pointing further to the collaboration that hidden truths involve. The novel’s Rosetta, her hair shorn and name changed to Ross Stone, hides in plain sight among a handful of boys from home.

Rosetta/Ross befriends another misfit, Will, whose uncertain sexuality and religious fervor cause clashes with other soldiers. “I wanted to have a friend who was also a kind of misfit,” McCabe says. “He revealed himself to me over the course of the writing. I just knew he was going to be different and didn’t fit in with the other boys.”

McCabe was plodding through writing another novel—one her own father called “workmanlike”—when Rosetta’s voice came to her. That night she wrote what became the novel’s opening scene of Rosetta and fellow soldiers posing for a photo: “The photo man, he makes us six press together like horses in a rainstorm.…Jeremiah’s hand rests on my shoulder and my arm is round his waist. My spine shivers like we’ve been caught kissing in church.”

The snapshot of a moment in time is at the heart of historical fiction, and McCabe vividly creates the grit and horror of war through solid research and imagination. She didn’t consult the real Rosetta’s letters again during writing of the first draft, but when she bumped up against something she couldn’t fully visualize, she looked to written history.

“I read a lot of letters from regular soldiers to get a sense of what they saw in battle,” she says. “But I was disappointed that often what I wanted to know wasn’t what the soldiers were willing to talk about.”

That goes double for the hidden female soldiers for whom few letters beyond Rosetta’s exist. “It’s amazing and sad,” McCabe says. “My guess is they were either afraid to be found out or already serving with their husband or father. Or the letters may have been destroyed.”

She read Sarah Emma Edmonds’ similarly themed memoir Nurse and Spy in the Union Army but was still left with unanswered questions. “What I wanted to know was how she did it and how she felt about it,” McCabe says. “She didn’t offer that.”

Instead McCabe had to look for snippets of truth, like the soldier who wore a ring made of bone found on the battlefield. “That spoke to how the war would affect certain people,” she says. “Depravity would become commonplace.”

Battle scenes were the toughest to write, McCabe says, but the results are both believable and powerful.

“It was a dark place to spend a lot of time,” she says. “I know what it’s like to be nervous or scared, but I don’t know what it’s like to be in that life-or-death situation. I had to think about what I would focus on in if in that experience: People cut down in lines, the horrific wounds, dead soldiers and dying horses—just chaos. It makes me have more admiration for soldiers who fight and then come back and try to live normal lives with families. How do they pull that off?”

McCabe is committed to writing historical fiction. “I love doing the research,” she says. “I learn a lot and it’s fascinating.”

Next up is a story inspired by a serial killer who has an adopted daughter.

“Another secret, right?” McCabe says.

Joe M. O’Connell, author of Evacuation Plan: A Novel from the Hospice, is based in Austin, Texas.