Greer Macallister’s historical novel Girl in Disguise (Sourcebooks) is a rollicking mashup of the real and imagined exploits of Kate Warne, the first female operative employed by the famed Pinkerton Detective Agency.

How did you come to write Girl in Disguise?

When I first heard Kate's story a few years ago, I was floored. This woman was such a pioneer. She was a female detective in the 1850s, when it was completely unheard-of, and she was so good at it that she was assigned by Allan Pinkerton to run her own division. She helped save Abraham Lincoln's life as he made his way to his inauguration. She was an undercover spy for the Union during the Civil War. Somebody needed to get her story out there, and I figured it might as well be me!

You mention in your author's note that very little is known about Kate Warne; there aren't even verified photos of her--partially because she was a spy and also because Pinkerton Agency records were lost during the Chicago Fire of 1871. How much of her story is based on historical sources and how much did you have to imagine?

Those gaps in the historical record made Kate the perfect subject for historical fiction--a little history and a lot of fiction. We know the facts on a handful of cases she worked, like the Adams Express case and one where she posed as a fortune-teller to catch a poisoner. Her role in thwarting the Lincoln assassination attempt in Baltimore is documented. But a lot of the rest is just open space, so I got to choose how to fill it in.

Were the lives of Warne's male colleagues--including Allan Pinkerton--similarly shrouded in mystery?

Not to the same degree, although some operatives' lives were better-documented than others. Pinkerton himself wrote and published a lot about his own prowess, so with him it's the opposite--tons of information, but not all reliable. For the cast of characters around Kate, I drew on some information about her real colleagues at the time, but mostly I combined and synthesized and created. It's all about balancing story and history to make the best possible experience for the reader.

Kate Warne is a mature woman, a widow, when she approaches Allan Pinkerton in 1856 and offers to work as a detective. Why then the title, Girl in Disguise?

Titles are always a challenge. It could just as easily be Woman in Disguise. But her male colleagues see her as a girl, for one thing, and she asks herself at one point whether she's a good girl disguising herself as a bad one or the other way around. I wanted that question to resonate.

You have now written two novels: the first, The Magician's Lie, is set in 1905, with a fictitious protagonist and fictitious events. The second, Girl in Disguise, is set in the Civil War era, and features actual historical personages and events mixed up with fictional characters and events. Which book was easier to write and why?

Girl in Disguise was definitely easier because I set myself a much more modest challenge. The Magician's Lie has a complicated structure, jumping back and forth between two timeframes in two voices, between these two-person, confined, almost claustrophobic scenes and a bigger, sweeping, epic story. Girl in Disguise covers several years, but it's straight forward, all with Kate in the forefront. And knowing what I needed to incorporate from history--I didn't set out to write a Civil War book, but the work she did during the war was essential to telling her story--helped me decide on the shape early on.

Will you continue to write about strong women in inconceivable situations?

Absolutely. I really feel like I've found my sweet spot with what I call the bad-ass women of history. Even if all I do is confine myself to writing novels inspired by unsung strong women who lived in America between 1850 and 1900, there are dozens--if not hundreds--more stories to tell.