France is a curious country. You can talk about anything here: about paedophilia, about the most shameful passions, but not about our families' dishonour during the second world war – because that particular past just won't pass. Especially if you argue that to have taken part in the worst atrocities of the Nazi occupation one didn't necessarily have to be a monster.

My novels have been read by hundreds of thousands of people in France over the past quarter of a century. I'm reputed to be a lightweight author, drunk on smiley sentimental literature. And then, at nearly 46 years of age – the age at which my father died – I confessed what my immoderate mirth was hiding all along and published a difficult, irrevocable book: Des gens très bien (Very Nice People). This 300-page crime novel, all of a sudden, sparked a crisis.

Why? Because it speaks of the blindness of my family and of our whole nation. Because it evokes the guilt of the upright, morally endowed people who collaborated with nazism and who, definitively, allowed the extermination of the Jews. Because it says that my grandfather was both a fundamentally decent chap and an accessory to utter evil – something our modern brains have a hard time grasping. Because it cries my shame at possessing the genes of a man who collaborated at the highest level.

At 17 I understood that on the day of the Vél d'Hiv roundup, when around 13,000 Jews were arrested in Paris (almost all of whom were exterminated), my grandfather Jean Jardin was the chief collaborator to the most collaborationist of French statesman (Pierre Laval, head of government under Marshal Pétain). At the time, he was the chief of staff in Vichy for the man who wished for "German victory". He was Laval's eyes, his right hand, his mouthpiece – if not his conscience.

Since then, consumed by shame, I have wondered how a perfectly decent man like him, belonging to a society of perfectly decent people, could aid the horror. My book is a log of my slow awakening. To burn down a synagogue and liquidate a few Jews, all you need is a handful of violent sadists. But to perpetrate this on a large scale, a moral discourse must be used of a sort that mobilises a great many decent people, who will be even more efficient. My grandfather, a man steeped in Christianity, was one of those people.

All this I screamed out in my book, hurling myself into truth so as not to die of blindness at the age of 46, like my father, who lived in anger at reality. And all of a sudden, a large section of the press – accustomed to the notion that crimes are the deeds of bastards – were up in arms. Le Figaro insulted me, publishing a vehement double-page spread in its magazine by an uncle of mine who remains loyal to the memory of Vichy.

Even Le Monde, imbued with its high moral authority, attempted to discredit my book while championing an obliging biographer who once sought to whitewash my grandfather. The two leading French newspapers insinuate that I have no evidence against my forebear – as though that were my object (why would I gratuitously smear my own lineage?), as though it weren't obvious that a head of government's chief of staff is an accessory to his superior's acts. They charge headlong at me, with ferocious contempt and hatred.

Why? Because my book talks above all about family, and therefore about all families that, to varying degrees, followed Marshal Pétain in 1940. As long as villainous ex-collaborationists were in the dock, then we were not personally affected. They were the bastards, not us, and certainly not our families. But here I bring up the accountability of people who believed they had moral standards, therefore I'm impugning the honour of our own families.

Now of course my readers will speak out in the debate. Very rapidly, other French media commentators will counter-attack, especially in the freesheets, the major radio stations and the big provincial press born of the French resistance, as well as the TV broadcasters that grab young people's attention. A fierce memorial battle is going to be fought between the older generation and the fortysomethings, who are not as submissive as their elders to their fathers. Much will be left unsaid, alas, for the older generation will never dare admit openly that to defend Jean Jardin amounts to defending Vichy.

But the lovely thing about France is that all this started with a book: an object which, in our land, remains sacred. Vive la France! The one to come, that is.

Translated from the French by Eric Rosencrantz, Presseurop

• this article was amended on 13 January 2011. Due to an editing error, the original referred to a "lightly apparelled" author. This has been corrected.