In the first book in Diana Gabaldon's fictional Outlander series, Claire Randall, on her second honeymoon with her husband in Scotland after World War II, visits Craigh na Dun, a make-believe prehistoric stone circle near Inverness, and falls through the stones—and into the 18th century.

Written in My Own Heart's Blood is the eighth—and latest—book in the series. In all, the Outlander books have cracked the New York Times Best Seller list six times and have sold more than 25 million copies worldwide, in 26 countries and 23 languages.

Well-drawn characters and vivid descriptions are part of Outlander's appeal, but Gabaldon's use of historically accurate details—aside from the time travel—also undergirds the plots. Through her writings, she's become an expert in 18th-century Scotland.

The long-awaited Outlander television show premieres tomorrow night at 9 p.m. on STARZ.

Coincidentally, National Geographic's August cover story, "The First Stonehenge," is about recently discovered Neolithic ruins in Scotland's Orkney Islands that, author Roff Smith writes, are "turning British prehistory on its head."

Gabaldon's story lines center on Scotland's ancient standing stones, so we asked her to give us a Scottish history lesson—Outlander style.

Our August story focuses on the Orkney Islands. Have you visited Orkney?

I actually just visited Orkney about 18 months ago. A guide we know in Scotland took us to a number of the places mentioned in the article. We went to Skara Brae and Maeshowe and the Ring of Brodgar, and all of that. Fascinating place!

When reading the NG Orkney story, did you connect it with Outlander at all?

Oh, yes, indeed. Not with the present book or the one I'm about to start working on, but to a different project. It will be a long time coming, but for a while now I've intended to write a book—or possibly more than one, as these things have a tendency to grow—about Master Raymond. He's the little apothecary Claire meets in Paris in Dragonfly in Amber [the second book in the series].

The moment I looked at Skara Brae, I said, OK, this is it. This book will focus on Master Raymond, and Orkney is part of his story. I don't know what the whole story is yet—I just feel this deep resonating connection with him in Orkney.

What resonated with you the most when you visited the Neolithic sites in Orkney?

The connection the culture had to the landscape. Orkney has the kind of landscape that sort of lends itself to a relationship with the people. I think that relationship is intensified because of its remoteness and the long periods of time when there was no interaction with other cultures.

One structure remaining in Orkney is the standing stones. You use a similar circle of stones as a time portal for your main character, Claire Randall. Why did you choose the stones for a time portal?

Originally, I was just going to write historical fiction, but at about the third day of writing, I introduced this English woman, just to see what she'd do. I loosed her into a cottage full of Scotsmen, and one of the men stood up and said, "My name is Dougal McKenzie, and who might you be?" Without stopping to think, I just typed, "My name is Claire Elizabeth Beauchamp, and who the hell are you?" And then I thought, "You don't sound at all like an 18th-century person." [Chuckles]

I fought with her for several pages, but she wasn't having any of this—she just kept making smart-ass modern remarks. She also took over and started telling the story herself, so I said, "Well, I'm not going to fight with you all the way through this book. Go ahead and be modern. I'll figure out how you got there later." So it's all her fault that there is time travel in these books!

I was doing a lot of research on Scotland at that point because I'd never been there and kept coming across the standing stone circles. Every time I'd read about the stone circles, it would describe how they worked as an astronomical observance. For example, some of the circles are oriented so that at the winter solstice the sun will strike a standing stone. But all the texts speculate that nobody knows what the actual function of these stone circles was. And so I began thinking, Well, I bet I can think of one. [Laughs]

In the Outlander universe, how did you make time travel seem plausible?

If you're going to write time travel stories, you have to sort of figure out how does time travel work in this particular universe that I'm dealing with.

There are lines of geomagnetic force running through the Earth's crust, and most of the time these run in opposing directions—forward and backward. In some places they deviate and will cross each other, and when that happens, you kind of get a geomagnetic mess going in all different directions. I call these vertices.

Essentially, it could be possible to have something like this nexus of crossing lines to create a little time vortex. And if you could have a person whose sensibility to geomagnetism is sufficiently advanced so that they can not only detect this but enter into it in some way, then you have a plausible way of time travel.

So if prehistoric people noticed that every so often when people crossed that particular patch of grass, they disappeared, it would cause considerable consternation, and they might think it worthwhile marking that spot. So that might be the reason why the stones are there, and why they're set up the way they are, as in, "People tended to disappear on the winter solstice when they step over here, so don't do that!"

I will have to do a write-up called the Gabaldon Theory of Time Travel. [Laughs]

How much research have you conducted for the Outlander series?

I'm not sure how you would quantify that. I've been doing research practically nonstop since I started writing. I do the research at the same time as I write, and it kind of feeds off itself. I would say I've been in a constant state of research for the past 24 years.

Can you give us a quick rundown on what history you have covered in your plot lines so far?

The story traces the political and physical revolution from the Jacobite rising all the way through the American Revolution. And on the other side of the time travel, we're dealing with World War II, and Claire's occasional flashbacks and knowledge of that war.

We began in 1743, just before the Jacobite rebellion and traced the climactic confrontation at Culloden, which crushed the clan system and all but destroyed the Highlands for a hundred years. We move on from there, as the Scots did, to America. That's because in the 1730s a large number of the Highland Scots had already immigrated and settled along the banks of the Cape Fear River [in present-day North Carolina]. By the late 1740s most of these earlier immigrants were settled and fairly prosperous, and kinship being what it was in the 18th century, you went where you had relatives.

A lot of Scots ended up settling in the mountains of North Carolina and Tennessee. And of course, these people were ideally placed to be in the middle of the American Revolution, and that's where Jamie and Claire are at the moment. At the time of the revolution, one in three colonists came from Scotland and, in fact, there were Scots fighting on both sides with great ferocity.

Was there ever a time when you purposefully wrote something you knew to be historically inaccurate?

Yes—only once that I can think of, and that was in Outlander [the first book]. I wanted to have a witch trial, but looking into it, I could see that the last witch trial in Scotland took place in 1722. So I was telling my husband that I'd really like a witch trial, but it doesn't fit. He looked at me and said, "You start right off with a book in which you expect people to believe that Stonehenge is a time machine, and you're worried that your witches are 20 years too late?" [Laughs] So I did stretch that point. I figured that possibly this witch trial was an ad hoc affair that didn't make it into the record. That's the only place where I can remember I deliberately moved something that I knew was not quite there.

Claire Randall goes back in time through the standing stones and immediately meets a band of Scottish Highland warriors. What was the clan system like in Scotland?

The clan system was very tribal. It was composed of extensive family units, and as it grew larger, the clans became political entities. And you didn't have to be born to a clan, you could come in and swear allegiance to your clan chief, and you'd become a MacKenzie or a Grant or whatever, and then you'd change your surname. People usually did this as a trade of armed service or farm service in return for food or land.

If the clan chief decided to declare war on someone, you had to bring whatever you owned in the way of a weapon. These tactics worked on a small level, but get in with the British army and you were in trouble.

The level of the clan chieftain was different than the system in England—it wasn't hereditary. The son of a chief might have the inside track, but the next chieftain was elected by consent of the senior clansmen present. So they sometimes got better leaders than the British did on a hereditary system.

That said, the system was good for the clan, but it wasn't necessarily good for Scotland. The way the clan system evolved was cellular: You had very strong people who couldn't lead more than their own clan without a lot of trouble.

Out of all the Highland clans, why did you choose Clan Fraser for the beloved character Jamie Fraser?

Through the course of my research, Jamie was just called Jamie Blank for a long time. I took Jamie from the name of a "Dr. Who" character who originally caused me to choose Scotland as my setting. I was reading a book for research called the Prince in the Heather, by Eric Linklater, which described what happened after Culloden. It said that, following the battle, 19 wounded Jacobite officers took refuge in the farmhouse by the side of the field. There they lay for two days with their wounds, unattended in pain. At the end of that time they were taken out and shot, except one man, a Fraser of the Master of Lovet's regiment, who survived the slaughter. And I was thinking that if I expect Jamie to survive Culloden then his last name better be Fraser.

A referendum on Scottish independence is coming up. Do you have thoughts on that because of your connection with your characters?

There's a line of philosophy in the events in my books to the events happening in Scotland now. That said, I'm very careful not to take a public view on it. It's not my country, so its not my business to be telling them what I think.

I have a number of Scottish friends from the Outlander TV show, all of whom are on the "yes" side. I was talking to them once, and I said, "You know, this is all well and good, democracy, etc., and it's a romantic idea too. But I've read a lot of Scottish history as of late, and you guys have never been able to cooperate about anything for longer than ten years at a stretch. You think you're going to do it now?"

This interview has been edited and condensed for clarity.