In Harrington’s An Inconvenient Duke (Sourcebooks Casablanca, Mar.), Marcus, a duke on a mission to avenge his sister’s murder, falls for Danielle, who secretly runs a charity for abused women.

Danielle has dedicated her life to helping women in danger. What inspired this socially conscious heroine?

It actually started with Marcus. The series is loosely based around comic book heroes. He is Captain America. In the second book, the hero is based loosely on Thor, and the third one is Spider-Man. I started with the heroes and then it was like, okay, who is going to be Captain America’s match? She has to be incredibly strong, courageous, and selfless. Danielle went through a couple of iterations before I landed on the one in the book who risks her life in secret because she doesn’t care about glory or fame. When I landed on that, I thought, “Yes, she is going to be all of that, and she is also going to be able to dance at a ball and know how to behave in society.”

What is most appealing to you about writing strong female characters who defy societal expectations?

It is exactly that: women who defy society. They are educated, confident, not afraid of speaking their minds. They always have a mission. They always need to have a job, a purpose in life. If they don’t have that from the very beginning, how does the reader ever connect with them? They can’t just be an heiress who is sitting around waiting to get married. My books are very modern. They all talk like modern Americans, and the heroines talk back in ways that they would never have done historically. That’s what makes it fun and what bridges the gap between the real Regency and what modern-day readers expect.

When Marcus wants to retreat from his life in London, he secludes himself in an old armory, which becomes his base of operations. Where did the idea for this unique getaway come from?

It originally started as an idea of having a gentlemen’s club, like White’s or Boodle’s, but just for men coming back from the war. The heroes were going to operate out of that, like Superman’s sanctuary. But that just seemed too slick and refined for these soldiers who had been through the roughest part of battle. So I put them in a building that represents war and the protection of the things they love. As the series goes on, the armory will become more refined. The duke fixes it up at the end of book one. They have got a training area, and they’ve got leather furniture and chandeliers. By the end of book three, some women will be coming into the armory. By the end of book four, they might even get an Alfred character, the butler from Batman.