* THE BOOK: SOFI Oksanen’s third novel Purge has proved such a stunning success it is being compared to the bestselling Dragon Tattoo trilogy of Swedish crime writer Stieg Larsson.

But I don’t think the comparison is particularly helpful for readers.

Yes, Oksanen tackles some of the same subject matters as Larsson – including sex trafficking and the abuse of women.

But The Girl with the Dragon Tattoo is structured like a classic whodunnit while Purge, strictly speaking, is not a crime novel.

Oksanen’s bestseller explores the relationship between Zara, a prostitute and murderer on the run from brutal traffickers, and Aliide Truu, who comes to Zara’s rescue when she shows up one night at her cottage, deep in an Estonian forest.

So far, a fairly straightforward beginning, but things get more complicated when the story splits across two periods of time.

The tale starts in the early 1990s when Zara arrives at Aliide’s cottage, but the focus then flits across the decades to explore Estonia’s – and Aliide’s – history.

Although the narrative jumps between the present and the past, there are consistent themes of love, treachery and the corruption of those in power and Oksanen ensures that the social and political history does not overshadow the story of the growing relationship between the two women.

The title of the novel refers to the mass deportation to Stalin’s gulags of those Estonians suspected of collaborating during the German occupation of 1941 to 1944.

But Oksanen is smart enough to anchor the narrative in the connection Zara makes with Aliide, rather than the political upheaval that throws them together.

Despite a slowish start to the story Oksanen’s expertise at creating an atmosphere of unease ensured I was keen to know more about how Zara had got herself into such terrible trouble – and why Aliide would be prepared to help.

It turns out that Zara is the granddaughter of an Estonian woman exiled to Siberia during the purge, and is on the run from Russian pimps after being trafficked via Berlin as a sex worker.

The traffickers, Pasha and Lavrenti, are closing in, but Aliide Truu is a formidable woman who will do her utmost to keep them at bay.

But what is Aliide’s back story?

Without giving too much away, the older woman’s past takes us back to the Soviet reoccupation of 1944 when the Germans fell to the Red Army.

Be warned – Oksanen’s novel is not for the fainthearted. It emerges that Aliide and her sister were sexually abused by the Communist militia during the war, so she has at least one good reason to sympathise with Zara’s plight.

Purge’s key theme appears to be that regime change is sometimes used by conquering forces to exploit weak individuals, particularly women. The main characters Zara and Aliide are very well drawn and the way they slowly grow closer makes the novel a satisfying read.

But Oksanen also explores the plight of Estonia in the 20th century, a disturbing history lesson I hadn’t bargained for, and it left me wanting to know more.

* THE AUTHOR: WITH her first novel, Stalin’s Cows, in 2003, Finnish-Estonian writer Sofi Oksanen was thrust into the leading group of young Finnish writers.

She followed up her success with second novel, Baby Jane, in 2005.

Oksanen was a drama student at Helsinki’s Theatre Academy before she turned to writing full-time and her first original play, Purge, was staged at the Finnish National Theatre in 2007 and got positive reviews.

The characters Oksanen created stayed with the author and out of the play grew her third novel, Purge, which was published in 2008.

The novel turned out to be the author’s big break – it became a number one bestseller in Finland, selling more than 170,000 copies. It also scooped a number of literary awards, including The Finlandia and The Nordic Council Literature Prize of 2010.

Purge – originally Puhdistus – was the first of Oksanen’s novels to be translated into English, and is now translated into 38 languages. The paperback edition published by Atlantic Books earlier this year contains a translation by Lola Rogers. Success came early for Oksanen as a writer – she was born in 1977 – and she now lives in Helsinki.

* Purge by Sofi Oksanen is published by Atlantic Books, priced £7.99, but you can get it half price at Waterstone’s in Oxford and Witney with the Book of The Month voucher printed every week in the Oxford Mail.