Holocaust chic or a true examination of good and evil?

There was always going to be a problem with The Reader. The novel by Bernhard Schlink, published in 1995, was the first in German fiction to humanise a concentration camp guard. Schlink's brave, semi-autobiographical narrative was attacked from the outset, and with good reason, for moral ambiguity.

Its hero is seduced in his teens in a small German town by a domineering bus conductor whom, as a law student, he later recognises as a defendant in a 1960s Auschwitz trial. At the heart of the story lies the recognition, painful to us all, that love is blind and sex takes no account of history.

Filmed by Stephen Daldry after a decade of dithering by the late Anthony Minghella (who was plainly disturbed by its material), the movie plays a dangerous game with our conscience. It casts Kate Winslet as Hanna, the former SS guard who initiates the narrator in the joys of sex in exchange for an immersion in an education she has somehow missed out on, no doubt due to her unpleasant duties during the war. The boy thinks it's a fair deal, and so do we.

Kate Winslet, though, is Kate Winslet. She gives an outstanding performance as her unmistakable self, heroine of Titanic, irresistible wife of cuddly Sam Mendes. We, the audience, cannot find it in our hearts to condemn Kate Winslet. Naked before the film is 15 minutes old, she lures us into a fatal web of sympathy and desire that, for the film's duration at least, earns Hanna's conundrum a credibility it does not deserve.

By picking so glamorous a heroine, Daldry manages to prove Schlink's case that sexual attraction suppresses moral judgment. Point taken. This, however is not any ordinary tale of a schoolboy being corrupted by an older woman with a dirty secret.

The dirty secret here is her part in nothing less than the murder of six million people, a number too large for the emotions to grasp and therefore suspended for the benefit of the characters we see on screen, Hanna and her lover. By pushing mass murder into the backdrop of the story, Daldry and Winslet lay themselves open to the charge of trivialising the greatest crime in history - a charge articulated by one syndicated critic at the Los Angeles first screening as creating a kind of "Holocaust chic".

The accusation is not without substance. There has been an unconscionable surge of Holocaust exploitation in recent years in works that range from the artless musical Imagine This!, which has just closed in London after a three-week run, to the sophisticated William Styron novel, Meryl Streep movie and Nicholas Maw opera known as Sophie's Choice, in which one woman's agonised dilemma in a Nazi concentration camp is vainly supposed to illustrate the greater atrocity. Sophie's choice is Holocaust chic.

There are even scenes in Stephen Spielberg's painfully faithful film of Thomas Keneally's documentary novel Schindler's List when the visual appeal of girls in a shower overwhelms our horror at the ambient outrage and allows a part of the mind to believe that maybe the holocaust wasn't so dreadful, after all. Anyone who makes art about the death of millions must first ask what the work adds to the sum of human understanding, and whether it does not perhaps, in some unforeseen way, diminish or - God forbid - normalise the victims' fate. If there is no ready answer to both questions, the work can be dismissed as exploitation.

The Reader is, its participants insist, an act of faith, a search for a compromised truth. After nine years Minghella and his production partner Sidney Pollack finally ceded the directing and writing in 2006 to the persistent Daldry and David Hare. The intended Hanna, Nicole Kidman, fell pregnant and dropped out. Then, last spring, Pollack and Minghella died within two months of each other and the project almost froze. But Schlink was on hand to urge the team on - he plays a cameo role in a beer-garden - and with Winslet in Kidman's place, a mixed cast of British and German actors played out the film in Germany without mishap.

At the trial, a law professor - Schlink's fictional alter ego - who observes the proceedings with weary fatalism is played by Bruno Ganz, who was last seen as the dying Adolf Hitler in Downfall. There was no shortage of relevance to the film or of realism. Former judges and lawyers at war crimes trials volunteered to play themselves.

The Reader is set in a land of silence, a country where no questions are asked. Germany in the 1950s was in the grip of an economic "miracle" that occluded the recent past. After the first Nuremburg trial of 21 major war criminals in 1946, and a few subsidiary trials that led to several dozen executions, the judicial process against Nazi offenders was suspended. There had been an outcry against the verdicts by German churches and the Americans, in particular, did not want to lose the loyalty of the West German government in their stand-offs with the Soviet Union.

Then, in 1961, an Israeli hit team in Argentina kidnapped Adolf Eichmann, one of the architects of genocide, who was put on trial in Jerusalem. The parade of evidence by camp survivors detailed not just the gassing and cremation at Auschwitz, the biggest killing centre but also the institutional cruelty that ran right through the Third Reich.

Hitler's personal doctor, Karl Brandt, directed the euthanasia of mental patients and medical experiments on children. Those involved in the mechanics of genocide included many of the German armed forces, the judiciary, the transport system and the civil service. Eichmann, a bureaucrat, was hanged.

Shamed by the Eichmann revelations, the Germans in 1963 put on trial in Frankfurt 22 lower-middle male functionaries from Auschwitz, most of them guards; six received life sentences. Few of the 3,500 female concentration camp guards employed by the Reich were ever brought to justice. The German trials ended in 1977.

The Reader takes an isolated instance and predicates it against the German pretence of not knowing. As a movie it aims to escape the charge of trivialisation by adopting an altogether serious, even professorial tone, which detaches the viewer from the emotional engagement demanded by Schindler's List.

David Hare's cautious script is delivered by the actors in faultless EFL - English as a Foreign Language. "Why don't you start by being honest with me?" must go down as one of the least appropriate lines ever uttered in the face of human horror. The two Jewish witnesses at Hanna's trial arouse less sympathy than their oppressor and Ralph Fiennes, as her lover grown old, looks aimlessly prosperous, untouched by experience. On many of these counts, the film is trivial as charged.

Its chief redeeming factor lies in the substance of Schlink's novel. In a language whose greatest living writer, Gunter Grass, was able only two years ago to admit that he had joined the Waffen-SS, Schlink, a Berlin law professor, broke the silence. He dared to write about the former Nazis who faded back into German society as quiet, efficient, invaluable public servants, contributors in the making of a united Europe. What, he demands, should they have done with the men who ran the trains to Auschwitz?

The return of war criminals, a theme explored in my own forthcoming novel, The Game of Opposites, is not just a German problem. It affects all of us, often in the least expected places.

Two weeks ago, a Conservative councillor in Croydon, of all blameless subsurbs, was made to resign after she was named as a sometime moll of a murderous IRA gangster. Who is to say that Maria Gatland had not atoned for her gun-running by serving a thousand hours on the Ways and Means Committee? Should she still be tarred with crimes of her teens, even if they led indirectly to city bombings? Is there no statute of limitations for youthful misguidance, no purification for a penitent soul?

These questions do prey on your mind after The Reader. The story itself errs on the side of unknowing. Schlink suggests that it is not up to you or me to confront a local perpetrator. We get on with our lives and let the justice mechanism take care of those it can find. What The Reader does is help us decide where to draw the line, and when to draw the curtains.

Schlink, the lawyer, has much to say about guilt and responsibility, individual and collective. His guard believed that superior orders relieved her of responsibility; her redemption comes through the acceptance of guilt. This is a seditious and irrational argument, the idea of exculpation by emotion. It has led the book to be condemned in some German publications as "cultural pornography".

More disturbing still is the theme of illiteracy, which Schlink employs as a metaphor for German amnesia: saw no evil, heard no evil, smelt no evil. Hanna makes her lover, and before him her camp victims, read to her aloud from Homer, Goethe and Chekhov.

The metaphor implies that reading books is a barrier against evil and learning to read an expiation of ignorance. But one has only to scan the catalogue of Hitler's private library to realise that the greatest murderer of all time was also among the best-read men. Books and movies are not necessarily a part of human enlightenment. It is the idea behind the word that makes it valid, or vacant.

Schlink has been accused by the American writer Cynthia Ozick, among others, of excusing the inexcusable. I disagree. Like Ozick, I was left extremely uncomfortable by reading and re-reading the book - it doesn't take long, only 218 pages - and I was shaken again by seeing the movie. Neither is a work you would want to take to a desert island but The Reader cannot be ignored. It challenges core definitions of good and evil.

It does not trivialise the Holocaust by any stretch of the imagination, nor does it glamorise the Nazi era. On the contrary: it requires you to start thinking for yourself, which is perhaps the most important lesson to arise from the century of tyranny and by far the best thing any of us can do when confronted by the forces of inhumanity in our lives.

The lesson of the Holocaust is that ignorance is no excuse. The Reader brings us face to face with how little we know about the people around us.

The Reader by Bernhard Schlink (Orion, £7.99).