Perhaps no other modern crime writer could have developed the eerie new historical novel Dominion other than C.J. Sansom. The Scottish-born novelist with a Ph.D. in history developed a strong following for his series of five Tudor-era novels about hunchbacked lawyer Matthew Shardlake. But for this massive alternative history of World War II, the author looked to the likes of Robert Harris’ thriller Fatherland for inspiration and in doing so, broke one of his primary rules: Never change historical fact.

“Basically, I’ve always been fascinated by the concept of alternative history,” Sansom explains. “What if one event or another that we know is very important turns out differently? What if John Wilkes Booth had not been able to get into Ford’s Theatre the night he shot Abraham Lincoln? More importantly, what happens to Great Britain if Winston Churchill does not become Prime Minister in 1940? That’s been rattling around in my head for years as the basis for a book. Although I knew it would be a big departure and something very different, I decided to leap off that cliff and I’m glad I did.”

Dominion is a sinister, atmospheric and breathless novel that Kirkus calls a “long, engaging bit of speculative fiction.” The book is set in 1952, the year that Sansom was born. As previously mentioned, a single moment of political struggle leads to Foreign Secretary Lord Halifax becoming Prime Minister instead of the Nazi-phobic Churchill, who would have fought to his last breath before surrendering the realm. Great Britain surrenders to Germany and has now lived more than a dozen years under authoritarian rule. In America, Pearl Harbor never happened and so the United States has retreated into an isolationist silence, while the bloody war in Russia continues unabated. An aging Adolph Hitler, deeply ill with Parkinson’s disease, struggles to hold together the Reich against enemies both foreign and domestic.

The plot, meanwhile, comes straight out of the shadowy world of John Le Carre or Sebastian Faulks. Civil servant David Fitzgerald uses his responsibilities in the Office of Dominions to spy for the British Resistance, led by a long-underground Churchill, while trying to protect his wife Sarah and his own dark secret: that he is of Jewish descent. When the resistance discovers that an institutionalized scientist named Frank Muncaster is carrying a war-redefining secret, they must plot to free him and get him out of the country. Hot on their heels is zealous Gestapo agent Gunther Hoss, a frightening hunter of men.

It all sounds very complex, and it is, but I make the point to the author that in his alternative history, he’s really only changed one fact. The entire head-spinning alternative world, from the well-kept secret of the Holocaust to the institutionalized anti-Semitism of a terrified Britain, is extrapolated from that single first change in leadership.

“That’s exactly it,” Sansom says excitedly. “I think the best alternative histories take one particular event and switch it round. Then you have to completely rebuild the world from there. It was particularly interesting to me because it was purely because Halifax felt he wasn’t up to the job that he gave up the role to Churchill. But Churchill never could have won the Premiership if Halifax had wanted it. I think it’s very likely that Halifax would have sought to make peace after France fell.”

Sansom also explained his view of the American isolationism portrayed in Dominion.

“The way I’ve imagined it is that Roosevelt, in 1940, faces a very strong isolationist movement,” he explains. “He has to be very careful in the amount of aid he gives to Britain. He wanted to give more than public opinion would allow, really. If the war is still going on in Europe and has to be faced as a fact, it’s more likely that Roosevelt gets elected. But if the war is over and there’s no chance that America is able to join in a war against Hitler in Europe because Britain is no longer available to use as a jumping-off point, I think that costs Roosevelt the election. Once in power, the isolationists would have taken a softer line with Japan and retreated within the continent.”

When we speak of Russia, meanwhile, I can’t help hearing that old advice lampooned in The Princess Bride: “Never get involved in a land war in Asia.”

“I think on any reasoning, given the technology of the time, the Germans never could have taken over Russia in the ‘40s or ‘50s,” Sansom says. “It’s just too hostile. Okay, if Britain had gotten out of the war, the Germans would have had more troops to send and they might have gotten further along in 1941 when they caught Stalin by surprise. But just as the Russians pushed back in the real world, they would have similarly pushed back in this alternative world. The Germans would also have faced a fierce partisan movement hiding in the woods.”

One of the most interesting aspects of the book is that its characters are drawn so very realistically. David Fitzgerald is no hard-hitting hero, and Gunther Hoss is no black-hat villain, as Sansom explains.

“I wanted David and his wife to be living embodiments of the problems people face with collaboration and resistance,” he says. “On one hand, if there is a totalitarian regime, you may hate it and want to resist. But on the other hand, if you want to keep your job and your family safe, that’s a very strong motivation for collaboration. I wanted to have David right on the cusp of that dilemma. He has every possible incentive to conceal the fact that he’s Jewish, but he can’t help feeling sympathy for what is happening to the Jews of Britain. He’s a very old-fashioned, conservative, honorable civil servant. He wants a quiet life with his family but he’s pushed the other way by his own decency.”

Hoss, on the other hand, was a key character to portray. It’s easy and common to portray Nazis, especially the Gestapo and S.S., as cartoonish villains out of an Indiana Jones movie, but Sansom decided to take a novel approach.

“It’s so easy to portray flat, one-dimensional characters,” he says. “There’s a standard figure in crime fiction that harkens back to Raymond Chandler, this disillusioned, rather shabby detective with a messy, unsuccessful private life. I thought about what it would mean if upon creating a character like him, instead of serving justice, he’s absolutely dedicated to this hideous cause. So I invented Gunther Hoss, who is a sort of down-on-his-heels policeman who, unlike most similar characters, is a totally convinced ideologue. He’s a total believer. That was my key to Gunther so that one could perhaps gain some sympathy for his disappointments and failures as a man, perhaps some admiration for his skill, but also be appalled by his carrying out of Nazi ideals.”

It’s a frightening world where world-shattering details are dropped indiscriminately—the “Final Solution” has already been carried out with icy efficiency, while Hitler’s ambitious scientists continue to institutionalize their research into eugenics and other pseudo-sciences. It’s a frightening path whose destination is meant to serve as a warning to today’s ideologues as well.

“I wanted to portray Britain becoming a semi-authoritarian state,” Sansom says. “I wanted to show it happening over time, because that’s often how it happens. Sometimes it happens overnight, as when you had the coup in Chile. But more often, there’s a slow, grinding pressure that goes on for years. It’s a turn of a screw and a turn of a screw and then you wake up and find yourself in a vice.”

As frightening as it is, Sansom—who like others, still refers to World War II as “The Good War”—refuses to give Hitler leave to continue his reign of terror.

“The other thing I was determined about was that the Nazi dream was going to fail and they were not going to win,” he says. “I think there’s good reason to think that events might have played out as I’ve portrayed them in my book. The Nazi state would have been hopelessly bogged down in Russia and Hitler really did have health problems, so there is every likelihood the whole awful mess would have collapses. I wondered how long that would take so I settled on 1952.”

Although his writing has slowed some as Sansom has struggled with some medical issues, readers will be happy to hear that the author is two-thirds of the way through a new Matthew Shardlake novel set in 1546 that portrays the end of Henry VIII’s reign and the struggle for control of the boy king who is set to inherit the realm. In the meantime, he’s very proud of the success of Dominion and is eager for it to hit American shores. Asked for any other messages he would care to broadcast, Sansom is thoughtful and characteristically to the point.

“I suppose the first message would be that this is genuinely how it could have turned out in Europe,” he says. “The second is to beware of people who put nationality ahead of other issues.”

Clayton Moore is a freelance writer, journalist, book critic, and prolific interviewer of other writers. His work appears in numerous newspapers, magazines, websites and other media. He is based in Boulder, Colorado.