American writer David Simon. He is searching for a cousin who he believes came to Australia after World War 2. Credit:Jason South ''Oh, would that be all right, Mr Simon?'' she says, a blush coming to her blush. ''Sure,'' he says again, with the same gruff good humour. Soon others are joining the queue for selfie-with-Simon pics of their own. David Simon is a writer's writer, a former investigative journalist with the Baltimore Sun who turned a year-long stint with that city's police force into the book Homicide: A Year on the Killing Streets, which spawned the TV series Homicide: Life on the Street. He is best known, though, for the five-season HBO series The Wire, which did for modern Baltimore what Dickens did for 19th-century London, capturing the city and its characters in minutely observed, and unflinchingly critical, detail. Though barely watched by the broader public in its first run (it has been a hit in repeats and on DVD), ''The Wire is porn for journalists,'' Simon says.

If that's true, its final season was hardcore: it focused on the newsroom of Simon's old paper, a place whose decline he mourns. ''At least this place feels like it's still got a pulse,'' he says, casting an appreciative eye around the newsroom. His more recent works have included a series about the Iraq war, Generation Kill, which was based on the reporting of another journalist, and Treme, which is set in post-Katrina New Orleans. In all his work, he combines the real and the fictional in a search for a greater truth: why is Baltimore in decay; what were the political and economic forces that made New Orleans so vulnerable. All your work is deeply rooted in the real, I observe, not very originally. ''That's a nice way of saying I don't have any imagination,'' he responds, half (but only half) jokingly. ''I tend to write either what I know or what I can acquire with great accuracy. And then I might say something fictional, or use fictional characters, but it's rooted in the reporting I did. ''I'm not a guy who conjures worlds that never existed. I'm not that kind of writer. I was trained as a journalist, and while I have to work as a dramatist to earn my bones now, my whole stock-in-trade is: 'Could this have happened? Am I being honest with the world as it is when I tell this story?''' Those questions loom larger than ever in his latest project, and despite his resistance to the pronoun ''I'', this time their import is personal. Simon is researching his family history, and that project has brought him to Australia.

''The fact the trail has gone to here is almost inevitable in a way,'' he says of his search for a cousin who, he believes, made it to Sydney from Europe near or just after the end of World War II. ''Australia actually has an incredibly proud history of taking in Holocaust survivors.'' Outside of Israel, he says, nowhere took as many by head of population. The man he's looking for is almost certainly dead now; the best Simon can hope for is to find someone who knew him, maybe the man's kids, or grandkids. But he knows he could be grasping at straws. What's his name? ''We don't know,'' he says. ''We think it may be Weiss, or some version of it, maybe Weiscz. He was the son of Esther Leibowitz, who married a man named Weiss. They were lost in the Holocaust, along with four daughters, and maybe one other son. But supposedly there was one child that made it to Australia." The most concrete piece of evidence he has of this man's existence is the memory of a distant relative - who recalls a visit to New York in the late 1960s or early '70s. The man who came looking for Aunty Helen, she remembered, had been pretty successful in the rag trade in Sydney. Beyond that, he says, ''I'm drawing a blank so far. The closest I have to a first name is Yossi or Yossel, but this is a pretty thin read.''

Does he have the makings of a book, perhaps, or another sprawling TV series of interlocking character arcs and storylines? ''It's something, it's something,'' he says. ''It's really percolating.'' It could, he admits, ''make a very bad book''. But in his hands, you suspect, it could equally make a very good one. In some ways, the rabbit hole he has disappeared down leads to the archetypal tale of the modern age, the refugee's tale of dislocation, of loss, of new starts. ''Dislocation is sort of the natural state of people now,'' he says. ''It's unnerving. And maybe there's a story in that.'' And if not, well, he has to pursue it anyway. He has no choice.

His father died in 2010, just before Simon's daughter was born. This genealogical quest is, he says, a form of kaddish (a prayer said over, and in honour of, the recently deceased). For anyone thinking of doing this with their own family, he has some simple advice. ''Start earlier than when you're 50. Because I'm struggling.'' kquinn@fairfaxmedia.com.au Twitter: @karlkwin