The Girl With the Dragon Tattoo, By Stieg Larsson

Posthumous debuts are rare, not least in the world of crime thrillers, where publishers want a brand for life, not an explosive one-off. Swedish journalist Stieg Larsson presented his publisher with three completed books before he died in 2005. Since then they have found success across much of Europe, which now looks to Scandinavia for its brutal murders, as it once did for its pop music.

The Millennium trilogy, of which The Girl With the Dragon Tattoo is the opening instalment, features a classic odd-couple duo: a crusading financial journalist, Mikael Blomkvist, and a freelance private investigator, Lisbeth Salander. Blomkvist bears a more-than-passing resemblance to Larsson himself, whose work exposing racism and fascism made him particularly unpopular with his country's far right.

Blomkvist is at a low ebb when an ageing businessman, Henrik Vanger, offers him a diversion. He wants him to spend a year writing the Vanger family history, while secretly investigating a cold case close to his heart: the disappearance of his 16-year-old grandniece, Harriet, over 30 years ago.

Blomkvist agrees, and decamps to the small island, three hours north of Stockholm, where Vanger lives, along with a handful of surviving family-members. These include Harald, a half-mad Nazi-sympathiser, Cecilia, his daughter, and Martin, Harriet's brother and currently CEO of the family business.

The case has intriguing aspects. On the day of the girl's disappearance in 1966, the bridge to the mainland was blocked by a traffic accident, and Hedeby Island itself was chock-a-block with Vangers present for a family dinner. It is, in Blomkvist's words, a "locked-room mystery in island format".

It's a fair analogy. The book feels closer to Agatha Christie than Henning Mankell, more concerned with the idea of detection as an intellectual exercise, like a crossword puzzle of human emotions, than a murky procedure compromised by the buffets and trials of real life. Nor is it a breakneck page-turner. It takes Blomkvist almost half the book to make any kind of breakthrough, when he spots something odd in a photograph of Harriet taken on the morning of her vanishing, and a series of coded numbers are revealed to him as that old serial killer standby, references to biblical chapter and verse.

Salander joins forces with Blomkvist for the novel's second half, a 24-year-old anorexic and bisexual loner with multiple piercings and tattoos, a history of mental illness, a photographic memory and some useful – and never explained – computer hacking skills.

She is at once a vision of female empowerment – a kind of goth-geek Pippi Longstocking – and an echoing agglomeration of clichés, not least in the scenes where she is viciously sexually assaulted by her mental health worker and proceeds to take her revenge. Her understandably pitiless view of men ties in with the grisly secrets that the duo's investigations unearth in the Vangers' past and present, and informs the later books, which deal with sex trafficking and government corruption.

If Larsson's book feels just a little amateurish, then perhaps that works to its advantage. This never feels like a by-the-numbers thriller. The twists and revelations work all the better for being worked for, rather than flung at the reader, two to a page.