Carmen and the conman

None of them would recognise the woman who rang the doorbell of psychiatrist Anne Darquier in 1963. Just three years previously, she'd attempted suicide, and here she was, an Australian in London, still needing help to come to terms with a fraught childhood, trapped in a job as a trainee clothes buyer for Marks & Spencer. "I was an utterly silent, quiet little girl. I know, I know, it's hard to believe," she says with a shriek of laughter.

But Anne Darquier had even deeper secrets. Over the next seven years, as they met for up to three hour-long sessions a week, she revealed far more of them than a therapist really ought to have done. "I knew that she hated her father, had been abandoned as a child and had a very tough childhood. I remember her saying, 'There are some people you can never forgive,' which struck me as a most untherapeutic remark."

In 1970, a week after Darquier had broken down in tears at their last session, Callil turned up at 38 Weymouth Street, London, for her usual Monday morning appointment and rang the bell. There was no answer. Upstairs, the psychiatrist lay dead on the bathroom floor. "Hers was not, I think, a deliberate suicide," says Callil. "She'd been drinking heavily and taking pills. It was probably more about stopping the pain than ending her life."

Darquier's dark secrets seemed to have died with her. For her part, Callil was back on an even keel. She's never been to a psychiatrist again, not even in the worst of times in the mid-1990s when Virago tore itself apart as an independent publishing house in a feud-ridden fury.

At her psychiatrist's funeral, Callil noticed she had been buried under a longer, more aristocratic-sounding name: Anne Darquier de Pellepoix. A year or so later, she saw that name again, when Max Ophls's film Le chagrin et la piti, about France under the Nazis, was shown on BBC2. Archive footage showed Reinhard Heydrich, Himmler's deputy and the man who convened the Wannsee Conference in January 1942 - where plans were drawn up to kill 11 million Jews - meeting France's most important collaborators at the Ritz in Paris. It was just four months after Wannsee, and Himmler had come there on the Fhrer's orders with one mission: to start the Final Solution in France.

The man filmed walking towards him, arm already outstretched for a handshake, would be especially useful: Louis Darquier de Pellepoix, head of the Vichy government's Commission for Jewish Affairs - and father of the 12-year-old Anne Darquier, then growing up in Oxfordshire, whom he'd never seen since she was a baby. Within a year he'd have the blood of tens of thousands of people on his hands. There are indeed some people one never can forgive.

The odd thing about Carmen Callil really isn't her temper. Maybe it was 20 years ago, when she was battling for her imprint's life, although even then, according to a former colleague, "a lot of the people she upset thoroughly deserved it". Her press cuttings may be full of vitriolic quotes about her (although the late Giles Gordon thought her "one of the last serious publishers in London"), but if there's any spikiness about the 67-year-old I meet in the Random House boardroom, it's inaccessibly buried beneath a thick layer of charm.

She is not, however, the tub-thumping saleswoman for her own book I'd expect her to be. Ask her about her emotions in writing Blind Faith and she veers off on a tangent about Israel's injustices against Palestine or Blair's folly on Iraq. Researching the book, she says, made her realise that in the late 1930s France was engaged in a civil war, which only ended with the Right's victory in 1940 - a broad-brush (and debatable) conclusion that doesn't remotely begin to do justice to a truly outstanding book.

Bad Faith is, as well being as good a history of French anti-Semitism as you will find, a superlative study of lies. In Louis Darquier de Pellepoix, the two overlap spectacularly. Where to begin? How about the "de Pellepoix" which Darquier appended to his real name to give himself the aura of a brave Gascon nobleman when in reality he couldn't trace any loftier ancestry than an early 19th-century chair porter.

From lying about making a fortune on the stock exchange (in reality he had swindled his employers) to lying about the money he was getting from the Nazis to lying about the fate of the 40,000 Jews whose deportations he ordered, the only consistent thing in Darquier's life was his mendacity. Astonishingly, it worked: he died in his bed, in Spain, in 1983, despite being exposed as a war criminal by an investigative journalist five years previously.

His wife Myrtle, an alcoholic and probable cocaine addict whom he routinely beat and to whom he was constantly unfaithful, was no better. Their marriage certificate, on which she shaved nine years off her age and gave a false name, was proof enough of that, quite apart from the fact that she was blithely committing bigamy at the time. Anne, whom they abandoned in England and never saw again together after she was six weeks old, was similarly fed a stream of lies - such as that her father was a Resistance hero, when in reality he was Vichy France's most outspoken anti-Semite.

More lies? Towards the end of the Third Republic the air was thick with them. Gilt-edged lies of anti-Semitism (Darquier soon sniffed out the money to be made by peddling hate) spread no matter how absurd. To Action Francaise, even Hitler was a Jew; to its leader Charles Maurras all Nazis were; to Henri Petit, not only was Jesus Christ not a Jew, he was an anti-Semite to boot.

Callil argues that the French taboo on digging up the dirt on the Vichy collaborators has long since been broken, although the story of her own researches into Louis Darquier seems to partially contradict that. Three research assistants pulled out of the project when they discovered what it was about and a number of French publishers turned down translation rights. Then there are the French historians' sins of omission: if they had really been so open about investigating their past, why is Callil able to throw new light on the cess-pit of far-Right networks in the 1930s, the expropriation of art treasures in the war and, most glaringly of all, write the first biography of the man at the very apex of French anti-Semitism?

Yet even though Callil is too modest (who, reading her cuttings, would have thought?) to give the hard sell, this is a stupendously well-researched book. Not only does it pull together a story of family deceit from France, England and Myrtle Darquier's native Australia, it shows how Darquier, already a proven conman and liar, moved into anti-Semitism because he could see that was where the big money lay. His lies mattered, as did those of other anti-Semites, like Maurras, because they were believed. Exaggerate the number of Jews living in France - say it's 850,000 rather than the actual 330,000 - and the Nazis, desperate to make up the numbers for the Auschwitz trains, started looking for more children to kill.

It took Callil eight years to research and write Bad Faith, which is, she says, "my life's work". Tracking anyone through the fog of war is hard enough, but with Darquier there were added complications: not only was she dealing with a conman but one who left surprisingly little trace behind in his contemporaries' memoirs. To uncover the whole truth about him, Callil spent a small fortune on researchers in France, Germany and Spain - "she'd certainly have spent more than her advance on research," one of her colleagues from her days at Virago tells me - as well as endless hours ploughing through the archives herself.

Without Anne Darquier, Callil certainly wouldn't have attempted any of this. But Anne knew her better than anyone. "Before I met her," says Callil, "I couldn't go out into the world at all. By the time I left her, I was out in the world, working away." If there's a debt there, it is one that this book repays spectacularly.

It took a lie - the fake surname "de Pellepoix" - to prompt Callil's search for truth, and in one of the nearly 100 pages of notes, Callil looks at the real Antoine Darquier de Pellepoix, an 18th-century aristocratic astronomer whom Louis Darquier falsely claimed was a relation. Looking at the heavens in 1779, de Pellepoix discovered a nebula to which he gave his name, Darquier's Nebula. Nebulae are the dying remains of stars, with a black hole at their dangerously unstable heart. And to the black hole and dangerously unstable heart of Vichy France, there is no better guide than the one Carmen Callil has provided in this magisterial book.

• Bad Faith, by Carmen Callil, is published by Jonathan Cape, priced 20.