Just as there is a tendency among the English to play down their achievements with self-deprecation, so is there a propensity among English novelists to rewrite their country's success as failure. World War II, Britain's finest hour, has inspired the richest creative license: Len Deighton's "SS-GB" saw a Britain conquered and occupied by Nazi Germany; Robert Harris' "Fatherland" opens in the week before Hitler's 75th birthday, and "The Windsor Faction" by D.J. Taylor imagined Wallis Simpson dying in 1936 and a pro-German Edward VIII remaining on the throne.

Now, with C.J. Sansom's "Dominion," comes another fiendishly concocted counterfactual history. It is 1952, 12 years after Britain surrendered to Nazi Germany after the brief 1939-40 conflict (which people called "the Dunkirk campaign or the Jews' war, according to political taste"). The vanquished nation, though not occupied, is led by Fascists — "Britain is still under their fist, Nazi fingers in every dark corner of the state."

But the underground Resistance is fighting back. Civil servant David Fitzgerald joins its ranks as a spy and is tasked with rescuing Frank Muncaster, a scientist in possession of vital information about America's atomic capability, and smuggling him out of the country. Unbeknown to the Resistance, Gestapo agent Gunther Hoth, a merciless hunter of Jews, is on a mission to foil Fitzgerald, smash his cell and whisk Frank off to Germany for interrogation.

Sansom's 2006 novel, "Winter in Madrid," garnered plaudits for its adroit blend of period detail and high thrills. "Dominion" is in the same league but picks up the pace and pads out into an alternative history on a grand scale. An ancient but still resilient Churchill heads the Resistance and is wanted dead or alive. Adlai Stevenson is in the White House. The "giant meat-grinder" that is the German-Soviet War has churned on for 11 years. The dead-end despair of sooty, foggy Britain, a "drab, conformist German satellite state," is expertly rendered, as is the determination of the Resistance fighters intent on restoring freedom and democracy.

Thanks to the cloak-and-dagger antics and cat-and-mouse chases, the novel's momentum never flags. Sansom also keeps our interest by rotating perspectives, taking us from Fitzgerald's point of view to that of his duped wife, Sarah, before jumping to Frank and then veering off to chart Hoth getting closer to his prey. There is an abundance of superb secondary characters, colorful backdrop figures from prostitutes to spiritualists, Blackshirts to Jive Boys, plus a cameo from a scene-stealing Churchill.

"Dominion" can be enjoyed as an exhilarating page-turner, but Sansom modulates the tone by inserting interludes that give the reader pause for thought. Meditations on empire, conquest, mental illness and the perils of nationalism edify, while scenes of street violence and mass Jewish roundups are sobering. Sansom injects a further strain of suspense into his narrative with the revelation that his hero, Fitzgerald, is in fact part Jewish and so should be wearing a yellow star and appear on the deportation lists. Secrets like this increase the urgency, complement the thrill of the chase and keep the reader absorbed until the frantic end.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Daily Beast. Born in Edinburgh, he lives in Berlin.