In 1988, Diana Gabaldon decided to write a practice novel. She called it "Outlander" and it, along with the subsequent five books in the series, went on to become an international bestseller. Last week saw the highly anticipated release of the seventh book, "An Echo in the Bone." The books are historical adventures featuring "time-crossed lovers" Jamie Fraser, an 18th-century Scottish rebel, and Claire Randall, his wife and a 20th-century English doctor. The novels time-travel between the centuries in Scotland, England and, in the more recent books, America. Gabaldon spoke with us from her home in Arizona.

Q The genesis of "Outlander" is known to many of your fans, but for new readers, can you explain how the series began?

A It all started with the rather vague notions conjured up by the image of a man in a kilt. I wrote "Outlander" in order to learn how to write a novel. I decided that for me, it would have to be historical fiction because I was a researcher in academics. I knew how to look things up. I decided on Scotland in the 18th century because at the time I'd just been watching an old "Doctor Who" episode and the Doctor had a Scotsman as his companion. He was my inspiration for Jamie.

Q And what about Claire?

A It's actually Claire's fault there's time travel in the books. As I was drafting "Outlander," this Englishwoman suddenly appears. I had no idea who she was or what she was doing in Scotland, so I turned her loose in a cottage full of Highlanders. She walked in and a man was puttering 'round the hearth. He turned and said, "My name's Dougal Mackenzie, and who might you be?" and without even stopping to think, I just typed "Claire Beauchamp Randall, and who the hell are you?"

Q So she asserted herself right away?

A Indeed. But she didn't sound at all like an 18th-century person. I fought with her for several pages, trying to beat her into shape and make her talk like an 18th-century person, but she wasn't having any of this. A few pages later, she took over and started telling the story herself. It was at that point I decided to let her be modern and I'd figure out later how she got to 18th-century Scotland.

Q It sounds as if you let your characters shape your plot as you write.

A Oh, yes. For me, characters basically fall into three categories: the mushrooms, the onions and the hard nuts -- sounds like a recipe for turkey stuffing, doesn't it? The mushroom is somebody who pops up immediately. I don't have to think about them. They're just there. An onion is someone whose presence I apprehend immediately, and as I work with them, I develop more of their layers. Those characters become, well, more pungent. Jamie and Claire are onions to me. The hard nuts are characters I'm kind of stuck with because of the circumstances, historical characters like Bonnie Prince Charlie. I had to hammer my way into him to learn what he's like.

Q What kinds of things can readers look forward to in the new book?

A The thing on the cover of the new book is a caltrop, an ancient military weapon. No matter which way you throw it, one of its four spikes is always pointing up. The new book has four story lines. They all intersect and they are all welded together by the events of the American Revolution. The first is Jamie and Claire's story. The second story line belongs to Brianna, Jamie and Claire's daughter, and Roger, her husband. They're in the future where they discover the Highlands of the 20th century are not any safer than the Highlands of the 18th -- but I won't tell you why. The third story line belongs to Lord John Grey and his stepson, William. Through this story line, readers will see the American Revolution from the English perspective, which is rarely presented to [American readers]. The fourth story line belongs to young Ian, Jamie's nephew, who has had a very difficult and tragic life.

Q In this book, you explore father and son relationships. What other thematic threads do you see as significant?

A Well, let's see; there are ongoing threads of conscience in all the books. To what extent is one obliged to take action knowing what you know? I think that's where the time-traveler element comes into play most. There's a lot about the nature of social obligation, of love and responsibility -- not just familial responsibility, but the responsibility one assumes for others. Under what circumstances is violence justified? Every character in these books deals with that one all the time.

Q Your books are philosophically and physically hefty. Do you begin with a plot outline?

A I don't write with an outline and I don't write in a straight line. I start where I can see things happening and so I write in bits and then I begin to fit the bits together. I do immense amounts of research as I'm writing. When I write this stuff, I live through it. I feel the cannon fire on a battlefield. I feel my flesh shake. ... I feel the echo in my bones.

Carole E. Barrowman reviews mysteries for the Star Tribune and blogs at carolebarrowman.com.