The novels for which Patricia Highsmith is likely to be remembered were published in the 1950s and 1960s, but they still have the power to disturb. Over the intervening 40 years, we have been surfeited with portrayals of nihilistic violence. The result is that we have grown blase. Even Bret Easton Ellis's gruesome depiction of affectless sadism in American Psycho has come to seem sufficiently tame to be made into a modishly vacuous movie. Yet there is something in Highsmith's portrayals of human motivation that continues to unsettle. They convey a sense of the inconsequence of morality in life that most readers - along with almost all of the film adaptations that have been made of her books - still find deeply threatening.
Graham Greene came as close as anyone has done to identifying the source of the unease that Highsmith's writings provoke when he called her "a poet of apprehension". There is not much violence in her stories and little of the concern with plot and clues of most writers of crime fiction. Highsmith does not write about crime in order to achieve a dramatic effect. She is interested in it for what it reveals of the flimsiness of ordinary life. She makes her characters drift or stumble into crime in order to show how easily their moral emotions are disoriented or put on one side. The mood of apprehension felt by many of Highsmith's characters expresses their suspicion - and her own considered conviction - that the moral framework of most people's lives is makeshift, a collection of stage props that is cleared away whenever things become difficult.
Highsmith's first novel, Strangers on a Train (1950) - one of the best she wrote and the only one to have been filmed convincingly (by Hitchcock in 1951) - features a conventionally decent young man, Guy Haines, emerging from a mistaken marriage. All he wants is a respectable career and married happiness with his new partner. A chance meeting with an unhappy wastrel leads, by a series of small but irrecoverable steps, to a place in which each agrees to commit a murder for the other. In the events that follow, Haines is forced to watch his familiar world crumble into pieces. He discovers he no longer knows what to expect of others, or even of himself. The story ends with Haines, deranged with guilt and fear, confessing to being a murderer to an indifferent drunk. If the story has a moral, it is that it could happen to almost anyone.
In Strangers on a Train, Highsmith's subject was the psychological disintegration of an average man. Her Ripley books have a seemingly different theme - the career of a man without the moral inhibitions of ordinary people. It has been said that Highsmith was fond of Tom Ripley, a part-time forger of paintings and occasional murderer, and it is true that her treatment of him is noticeably more indulgent in the later of the five books in the series. But in making Ripley attractive - sensitive to beauty, considerate to others in his everyday dealings, courageous and resourceful and endowed with an acute awareness of mood and place - Highsmith was not romanticising villainy; she was presenting a fact of life that moralists prefer to forget.
The qualities that enable people to live an interesting and fulfilling life - and that make them valuable to others - are not all of one piece, and what are usually seen as the distinctively moral virtues are not always among them. Moral virtue is only a part of what makes life worth living, and not always the most important part. That Ripley is a murderer does not prevent him leading a pleasant and civilised life in a quiet French town. Indeed, it was murder that made this life possible for him. Crucially, as Highsmith portrays him, Ripley is never troubled by the slightest sense of guilt.
The subject of Highsmith's novel, The Talented Mr Ripley, is the insignificance of conscience in the larger scheme of human life. It is a theme entirely lacking in Anthony Minghella's Ripley, who is gauche and insecure, a pathetic figure who is moved to murder by repressed homosexual infatuation and stricken with remorse when dreaming of his act. He suffers from a peculiar complaint of the 1990s: he is unsure who or what he is, or wants to be. He impersonates his victim in order to acquire an identity that he would not otherwise have. Minghella's Ripley is not amoral so much as sexually and socially confused.
In contrast, Highsmith's Ripley is not a repressed gay. He has slight sexual interest in men or women. He suffers as little from sexual repression as he does from guilt or remorse. Nor is he in search of an identity. He murders his acquaintance in order to gain access to his money and impersonates him in order to cover up the murder. If Highsmith's Ripley has a single, overriding motive, it is not the quest for identity. Ripley knows exactly what he wants and who he means to be. The book's achievement - largely preserved in Rene Clement's Plein Soleil (1959), despite its cop-out ending - is to show how an amoral character can contrive (with a bit of luck) to live well on a foundation of crime.
Highsmith's books have never sold in her native America. It is not hard to see why. Highsmith is not a writer who criticises conventional values for the sake of a higher morality. She attacks morality itself. In Strangers on a Train, Guy Haines is ruined by his innocent decency, whereas Tom Ripley thrives on his lack of it. The basic truth that these novels convey is the same: the real business of life goes on regardless of our moral sensations.
Playing with stylish sadism and designer violence is commonplace. Nihilism has become just another commodity in consumer culture. Highsmith's vision of the mere indifference of moral rules and judgements seems still too uncomfortable for a mass market.
John Gray's most recent book is False Dawn: the delusions of global capitalism (Granta, £8.99). Other essays in this series, on J G Ballard, Georges Simenon and Mervyn Peake, can be found on the NS website: www.newstatesman.co.uk