The essential first step to appreciating Stieg Larsson is to rid yourself of any fixed image you have of Swedish crime fiction. Yes, Larsson is a Swede, as is Henning Mankell and any number of other first-class spinners of mysteries. But the adventures of Inspector Kurt Wallander are far away from Larsson's novels. If Mankell is Swedish gloomy, Larrsson is Swedish noir. Very.

The other hurdle to overcome is to divorce Larsson's novels from reference to his life or, rather, his death. Would Larsson be receiving so much attention if his Millennium Trilogy - the second of which, The Girl who Played with Fire, appears in English this week - were not accompanied by the sad but romantic story of the author himself? Larsson handed the three novels to his Swedish publisher together, in 2004. Not long afterwards, and before publication of the first, The Girl With the Dragon Tattoo, he died of a heart attack, aged just 50. He did not live to see the extraordinary phenomenon that the books have become, translated into many languages and winner of countless awards.

The first of the trilogy had Mikael Blomkvist, a financial journalist and part-owner of the campaigning journal Millennium, taking an enforced break from his job after losing a serious defamation case. (There are similarities, though not to be taken too far: Larsson himself was famous in Sweden as a committed left-wing writer and commentator dedicated to fighting fascism and racism.) Blomkvist is hired by an industrial tycoon to investigate the unsolved disappearance of his young niece from the family's island home, 40 years before. In the course of his inquiries, he teams up with Lisbeth Salander - she of the tattoo in the title. With her help he solves the mystery. A strange, unlikely attachment forms. I recommend those new to Larsson to read the trilogy in order; knowledge of the first adds to the understanding of its successor.

In Tattoo, Salander played sidekick to Blomkvist. In Fire, she has the more central role. She's a heroine like no other in crime fiction. Teeming with psychological problems, anorexic, a victim of rape and all manner of sexual abuse, she spent her teenage years in disturbed rebellion. She dresses punk and has facial jewellery. A loner, bisexual, cold, suspicious of everyone, scheming and manipulative, she would be defined as a psychopathic personality, perhaps a sufferer of Asperger's syndrome.

Now in her mid-twenties, she's been officially declared incompetent to conduct her own affairs, yet has turned out to be, as we learnt in the first novel, a brilliant researcher and investigator, and a near genius at hacking into other people's computers. She also usefully happens to be skilled in many of the arts that inflict maximum violence, and even death, on others; she can absorb a high degree of pain.

To sum up, she's unbelievable. All her attributes are exaggerated, at times veering to fantasy; her mental and physical strengths are beyond those of ordinary humans. Yet Larsson's writing manages to make her intriguing, admirable and even - though this is an effort - sympathetic.

In Fire Salander returns to Sweden after an adventurous year abroad, having dumped Blomkvist without explanation before leaving. He is back in charge at Millennium. The journal is about to publish an exposé of sex trafficking into Sweden from Russia and other countries. The two authors of the articles and of a follow-up book are to reveal details of rampant under-age prostitution, and to name its organisers and users - who include senior policemen.

Shortly before publication the two are shot dead. The Colt Magnum used to kill them is found to belong to the lawyer who had been Salander's guardian and had abused his position by raping her. The fingerprints on the gun are Salander's. Not long afterwards the lawyer himself is also shot dead. Salander is now the chief suspect of triple murder. The police launch a nationwide hunt for her, backed by a sensationalist media campaign growing in hysteria as more emerges, much of it false, about her wild, troubled past. Blomkvist is convinced of her innocence, but his efforts to persuade her to co-operate with him in finding the real murderers are rebuffed. Evading the police search, she conducts her own inquiries, but does give Blomkvist one lead - the name Zala. The Girl who Played with Fire becomes an absorbing, exciting and bloody multi-layered chase involving Salander, Blomkvist, the police and a variety of unpleasant and sadistic criminals. The climax is a feast of gore.

The novel is complex in plot and characterisation, perhaps unnecessarily so. But the urgency of Larsson's prose prevents boredom in reading a book that would otherwise be regarded as over-long and over-crammed. Somehow, Larsson has managed to write a riveting read.

The Girl who played with Fire by Stieg Larsson
Maclehose, £16.99; 576pp Buy the book

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