The Nazis are too much with us, and we wonder why. Is it that, as one Frankfurt newspaper asked, Hitler is really "the Hero of the Seventies?" Or that, for too long, a persuasive and durable personification of evil, of evil unmitigated, has been lacking? Satan is demode, but Hitler is always news.

Len Deighton's new thriller inventively revises the facts on which the Nazi vogue is based. It postulates a successful German occupation of Britain in 1940 -- with Churchill executed and King George VI in the Tower of London.

Joseph Kennedy is U.S. ambassador. There are Focke-Wurf airliners playing between London and New York; an SS hospital at Hyde Park Corner; fried-turnip vendors in Marylebone; mail-order English courses for German troops; and German bands playing "Greensleeves."

New fates for famous men mingle with old fates for fictive ones. Churchill, facing a Luftwaffe firing squad in Berlin, refuses the blindfold and gives the V sign. DeGaulle, sucked by peace into nonentity, isn't even on the Primary Arrest List. But the imaginary General Fritz Kellerman ("a rubicund complexion and a slight plumpness") -- the senior SS and police leader for Britain -- and Standartenfuhrer Huth of Himmler's personal staff, wage their private, demurely vicious personal war to the death, as fictional characters should.

Such is the madcap escapist mood of "SS-GB": We're sick of the serious truth which, often enough, proves a mish-mash of guesses at the unknowable, so let's have a caper that thrills and maybe even heals, and more profoundly becomes an exercise in mental agility. It is a venerable tradition.

Quite early in the 12th century, Geoffrey Arthur wrote about Britain's pre-Christian kings, about whom he knew nothing at all. That's how, in the long run, William Shakespeare got to hear about Kings Lear and Cymbeline who then took on a new lease of life: real men whose fake lives have become more real to us than kings about whom we know far too much.

Deighton joins this tradition of virtuoso re-runs. Romans tinker with Greek materials, medieval writers rearrange romance, Shelley and Gide unite "Prometheus Unbound," Mallarme revamps "Hamlet," and Goethe and Thomas Mann the historical Faustus. In our century, to take only one example, Beryl Bainbridge gifts Adolph Hitler with a formative youth in Liverpool.

The process is that of literature gnawing shark-like on itself and mauling other entities as well, as we are still trying to digest the trauma of World War II. The tragedy is over; some of the scapegoats have survived and now savor what might have been, in a mood of masochism mingled with disbelief and not-quitemuted terror. But pseudology -- the science or art of lying -- is a balm that lets us grin as well, even about Hitler in his gruesome heyday. And the fact that we might need to grin -- or even frolic in Armageddon -- makes us think as well.

Deighton's pseudology centers on Superintendent Archer of Scotland Yard, a widower, educated at Christ Church, Oxford, and fond of "dark shirts and the sort of wide-brimmed hat he'd seen on George Raft in a Hollywood gangster film." Scheming and bumbling, Archer works dutifully alongside his SS opposite number and becomes a small study in not so much divided loyalties as degraded ones.

The fulcrum of the whole thing, however, is the Nazi rush to perfect an atom bomb in a remote seaside installation, and from this Deighton develops an intricately played multiple hand of jokers, trade-offs, double agents, double-cross, and ultra-canny trumps. Most mysterious of all is Mayhew, the laid-back rabid patriot, who wants the ailing kind dead rather than free; most memorable the fish-and-chips police state Britain has become; and most suspicious a civil service chief, Sir Robert Benson, who truncates New College, Oxford, to "New," which is a slip only an impostor would make.

Lewis Carroll might have called the book "Deutschland Uber Alice." Its premises are more memorable than what's built on them, and the so-called facts of history -- seen darkly through revisionist caricatures -- still have more appeal than the tracts of wooden dialogue under which it sags.

Had the Nazis occupied England, English-born Deighton might not have survived. Had his pretended ghost written it, "SS-GB" might have been more poignant, and more severe, a vision of promise burned and plentitude befouled in a green and pleasant land where birth made you eligible for the Hitler Youth and old age, infirmity or handicap made you eligible for something else.

Somehow Deighton isn't moved by his hypothesis, and we are closer to sick-sour Vaudeville -- say, Noel Coward in Auschwitz -- than we need to be -- even when heeding the pseudological imperative. "SS-GB" is an interesting symptom all the same, easing nightmare into thriller. History thus denied gives Geoffrey of Monmouth an extra, post-Christian British king -- Adolph the First.