Only after his grandfather committed suicide in 1980 in the throes of cancer did Mendelsohn discover that the strange, ostrich-skin billfold his grandfather had carried around in his breast pocket ever since the war contained a series of letters from Shmiel, dated 1939. They were desperate appeals to his American relatives to help his family escape to the US.

'We didn't know anything about this guy, so it was so uncanny afterwards to hear this man's voice crying out for help,' says Mendelsohn, now a classics scholar and one of America's most respected literary journalists. 'It seemed to suggest that my grandfather lived his whole life tormented by terrible guilt - otherwise why would he carry these letters?'

In 2001, Mendelsohn travelled to Shmiel's hometown of Bolekhiv (formerly known as Bolechow) in Ukraine to see whether any of its elderly inhabitants remembered his ancestors. So began the five-year odyssey recounted in his book The Lost: A Search for Six of Six Million, in which Mendelsohn journeyed to Sydney, Tel Aviv, Copenhagen and Stockholm, interviewing 12 of the 48 Bolechow Jews who survived the Holocaust (from the town's original Jewish population of 6,000).

On the phone from New York, Mendelsohn, 46, discusses The Lost with the same relaxed, unaffected eloquence that marks his celebrated New York Review of Books essays. It's not surprising to learn that he's speaking from bed - nor that it's from there, reclining amid pillows with his laptop, that he begins his essays - 'to trick myself into writing'.

If his literary criticism echoes the urbane, conversational style of the late film critic Pauline Kael, it's former New Yorker journalist Janet Malcolm's - in her fascination with the agendas and biases in the stories people tell about the past - that Mendelsohn's technique in The Lost most closely resembles. He approaches his subject as a literary critic, exploring how narratives are constructed, rather than as a conventional historian, seeking to master the past. 'A book, especially a fat, 500- page book, gives an appearance of totality,' says Mendelsohn. 'But what I want is to keep reminding people that this totality is illusive.'

The Lost is by turns a travelogue, a historical fact-finding mission and a suspenseful detective inquiry. It has been hailed as a major work of Holocaust writing in the US, with critics lauding Mendelsohn for offering a new way of grappling with the inconceivable events. But Mendelsohn resists this interpretation.

'This is not a book about the Holocaust,' he says. 'This is a book about how to write a book about the Holocaust. This is a book about people in the present confronting the past. The intense focus on my experiences - as I'm undergoing this worldwide, years-long search - is meant to remind the reader that the story of the past is something that was constructed in the present.'

There's a compelling moment in The Lost when Melbourne ex-Bolechower Meg Grossbard - once the closest friend of Shmiel's daughter, Frydka - lays down a condition for being interviewed: she will share her memories of Mendelsohn's lost relatives, but anything touching on her own wartime experiences would be strictly off the record. 'You think you deserve to know this because it's history with a capital 'H',' Mendelsohn recalls her saying. 'But this was my life. If I tell you my story, it will become your story.' During a four-hour interview, she relayed horrifying tales about the war - stories which, as Mendelsohn provocatively reminds the reader, he can't share.

Most non-fiction authors wouldn't bother mentioning parts of their investigations that fail to advance the story. But Mendelsohn is as much concerned with what is unknowable about his ancestors as he is with exhuming the residues of their lives. Grossbard's determination to cling possessively to her survival story testifies to Mendelsohn's theme: 'that the concreteness, the authenticity, of an experience cannot be duplicated, cannot be imagined, and that whenever it is, it's somewhat eroded or diminished'. He describes Grossbard as a 'figure of resistance of narrative - the story that won't be told, not because it doesn't exist, but because the person doesn't want to tell you'.

At a point in history when the survivors are passing on, Mendelsohn wanted to explore what happens to the memory of the Shoah, or Holocaust, when the protagonists are no longer alive. 'The book is obsessed with narrative: the narratives of survivors - what they tell you, what they leave out, what you find out later - and how you tell the story of people who can't tell their own story,' he says.

As The Lost reveals, five of the 12 ex- Bolechow Jews that Mendelsohn interviewed have since died. Through researching The Lost, Mendelsohn not only grew closer to his dead relatives, but also his younger brother, Matt - a professional photographer, who accompanied him on his travels, taking the enigmatic black-and-white photographs dispersed throughout the text.

While speculating about the possible fraternal tensions between his grandfather and Shmiel, which perhaps explain his failure to adequately respond to Shmiel's pleas, Mendelsohn recalls his own boyhood rivalry with Matt. At the age of 10, Daniel broke his brother's arm in a fit of jealousy. 'I talk about my relationship with Matt, not to regale the reader with dirty family laundry, but because that is a tool to think about Shmiel,' he says.

Readers not paying close attention will be puzzled by some of Matt's photographs, which Mendelsohn leaves uncaptioned, and often positions at unlikely points, in an effort to wean readers away from the tendency to be complacent about photographs in books.

'Often there's a photo section in the middle, and you breeze through and think, 'Oh yes',' says Mendelsohn. 'This is a book about piecing people together from the very tiny fragments that are left, and you have to pay attention to every one. That's how we know about history - painstakingly and sometimes tediously.'

No less audacious are the long passages of commentary on the Torah (the first five books of the Bible), which Mendelsohn interpolates throughout.

'I thought it was intellectually important to give a framework for thinking about the ethical, moral and emotional issues that were arising in a more abstract way,' he says. 'I began to see how aspects of Genesis related to my story. I thought: this is what the Noah story is about. It's about what happens when the world disappears and a few survivors hold themselves together and go on living.'

Mendelsohn draws on the biblical tale of the brothers Cain and Abel to throw light on his grandfather's relationship with Shmiel, and to explain the tensions between the Jewish and Ukrainian residents of Bolechow. The Ukrainians were so thoroughly enmeshed with their Jewish neighbours that many spoke Yiddish. Yet with the ascent of fascism, they turned on them with a primal ferocity.

'The Germans had this abstract need, so to speak, to get rid of the Jews, and they did it ultimately in an abstract way - the death camps,' he says. 'But the kind of killing you got in small towns, when neighbours were turning on neighbours, was of a savagery that betrayed a particular emotional content. It was the kind of violence you do to people you have a personal connection to. There was nothing abstract about it.'

Sydney Holocaust survivor Jack Greene, who once dated Shmiel's daughter, Ruchele, was moved by the emotional depth of Mendelsohn's account of his native town. 'He understands the position of the people in Bolechow at the time,' says the 81-year-old Greene. 'I've read quite a few books about the Holocaust, and he would be the first - or one of the very few - who expresses the feelings of the people, rather than just the historical happenings.'

Mendelsohn says that by reanimating his dead relatives, he has finally expiated his family's lingering guilt.

'My reason for writing the book was to confront at last, as best I could, a family mystery that had tormented many of us for a long time,' he says. 'In a metaphorical sense, I'm saving them 60 years later by restoring to them some sense of who they were.'

WRITER'S NOTES

Genre Literary fiction

Latest book The Lost: A Search for Six of Six Million (Harper Collins, HK$218)

Age 46

Born Long Island, New York

Family Mendelsohn, who is gay, is a father figure to the two sons of a friend

Lives New York City; Trenton, NJ

Education BA in classics from the University of Virginia; MA and PhD in classics from Princeton

Other works The Elusive Embrace: Desire and the Riddle of Identity (Knopf, 1999); Gender and the City in Euripides' Political Plays (Oxford University Press, 2003)

Other jobs Lecturer in classics at Princeton, currently Charles Ranlett Flint Professor of Humanities at Bard College

Next project A translation of the poems of the Greek poet Constantine P. Cavafy

What the papers say '[The Lost is] a vast, highly coloured tapestry. Indeed, with passion and no little grit, he weaves in snippets of language, fragments of incident, fleeting names - and succeeds in assembling an immensely human tableau in which each witness has a face and each face a story and destiny.' - The Washington Post

author's bookshelf

The Radetsky March by Joseph Roth

'This rich, sardonic tale of an Austro-Hungarian family's rise and rather haphazard fall over three generations is an absolute must for anyone with an inherited (like me) or acquired taste for Mitteleuropa and its tragically complex culture.'

The Leopard by Guiseppe Tomasi di Lampedusa

'Like the better-known The French Lieutenant's Woman, this is a 19th-century novel written well into the 20th century - quite appropriate for the tartly wrenching story of a Sicilian prince who knows he's missed his moment in history.'

Beyond Black by Hilary Mantel

'A subtle masterpiece by this contemporary British mistress of many moods: the oddly mesmerising story creates a completely persuasive world peopled by pesky ghosts - including Princess Di.'

Austerlitz by W.G. Sebald

'The greatest of the late German author's eerie, photograph-haunted fictions about displaced and disoriented characters in hopeless search of their own (and our) pasts, this one follows the quest of a man who grew up Welsh but turns out to have been a Kindertransport child from Prague.'

Howard's End by E.M. Forster

'Forster's awareness that a life of pure artistic sensibility is only part of the picture - the other part being the people who make the world run - is what makes him refreshingly, bracingly modern.'