“The Tattooist of Auschwitz,” a novel published in the United States by HarperCollins in September, tells the extraordinary tale of Lali Sokolov, a Slovakian Jew, who was imprisoned at Auschwitz in 1942, and forced to tattoo numbers onto the arms of thousands of incoming prisoners.

At the camp, Sokolov met a Slovakian girl and they fell in love.

Written by first-time author Heather Morris, based here in Melbourne, the book has seemingly come out of nowhere to be translated into 17 languages, with rights sold in 43 countries.

In the United States, there are half a million copies in print, and the book just hit No. 1 on The New York Times paperback fiction list.

What’s most extraordinary about this unlikely love story is that it’s mostly true.

The real-life Sokolov was a tattooist at Auschwitz, and he met Gita Furman there. The couple later married and moved to Melbourne, where they raised a son.

Morris interviewed Sokolov over several years before his death in 2006, and initially wrote a screenplay about his life. She later turned the screenplay into a novel.

An “Additional Information” section at the back of the novel offers basic facts about the story and adds gravitas to the book.

Interestingly, the section raises questions about how we talk about what is true in a novel based on a true story.

Does truth lie in the small details or the large events? Who is the arbiter? And what does fiction gain when it is said to be based on truth?

In the novel’s key scene, Sokolov first meets Furman when she comes to the front of his line and he must hold her arm and begin her tattoo: 3 then 4 – 9 – 0 – 2. She attempts to speak but he hushes her. Then, he looks into her eyes and falls in love.

From this key moment, everything follows.

In the Additional Information section Morris writes that 34902 was, in fact, Furman’s number. As it turns out, it’s not.

In a 1996 interview with the USC Shoah Foundation, Furman said her number was 4562. Other evidence from her own account and from the archives at the Auschwitz-Birkenau Memorial and Museum supports her claim.

Likewise Furman’s arrival date is said to be April 13, 1942. It’s not possible for a woman assigned the number 34902 to have arrived at Auschwitz on that date or even in that year. A woman entering Auschwitz at that time would have had a four-digit number.

Much of the interest in, and marketing of, the book focuses on the true story it is based on, yet there is some confusion, too, about which stories in the novel are true and which are not.

Morris said that the tattoo scene where Sokolov so momentously saw Furman for the first time occurred. Interviews with Sokolov and Furman from the 1990s, and with their son Gary recently, provide no support for that claim.

Why was Furman’s number in the novel also included in the book’s fact section?

Morris said Sokolov told her Furman’s number was 34902. Why did she take Sokolov’s word over Furman’s about Furman’s number?

“The book does not claim to be an academic historical piece of nonfiction, I’ll leave that to the academics and historians,” she wrote in an email. “It is Lali’s story. I make mention of history and memory waltzing together and straining to part, it must be accepted after 60 years this can happen but I am confident of Lali’s telling of his story, only he could tell it and others may have a different understanding of that time but that is their understanding, I have written Lali’s.”

Readers have loved “The Tattooist of Auschwitz” because it is based on a true story.

“There’s a real interest in fiction that is based on history and real people,” said Sara Nelson, a vice president, executive editor and special adviser to the publisher of Harper, an imprint of HarperCollins, who called the book an unusual hybrid of memoir and historical fiction.

“What readers get is almost a memoir,” she said. “They get the sense that they know this person and they walked through this person’s life with them.”

She also said, “It’s a novel so it didn’t need to be fact-checked, though a novel needs to have verisimilitude.”

Gary Sokolov, the son of Lali and Gita, said his dad was a survivor.

In the last year, Gary has been contacted by many readers of Morris’ book, Jewish and non-Jewish.

“So many people all over the world telling me of the positive impact it’s had on them,” he said.

He plans to produce more work based on his father’s life. He is in conversation with a producer about creating a musical.

“The fact that my dad, so many decades later, can have such a positive impact on humanity is just phenomenal,” he said.

Every author who turns fact into fiction must find a way to compress time, to omit events that don’t advance the story, and to be economical with the number of characters.

They must also solve tricky problems that are peculiar to their story, and for many, Morris’ choices have created a compelling and uplifting tale.

The history in historical fiction still matters, from small personal details (Gary Sokolov said it bothered him that his father’s name was misspelled “Lale” in the book) to larger complexities that may make a tale more murky.

Is there is a greater imperative for novels about an event as catastrophic as the Holocaust to get basic facts right?

The misrepresentation of Furman’s number doesn’t change her story — she was imprisoned at Auschwitz from 1942 to 1945, and she met her future husband there.

For readers who know something about the Auschwitz number system, especially readers who were there, the seemingly pointless error will give them pause.

It also undermines the credibility of other stories, like Sokolov’s tale about a soccer match between prisoners and guards.

One reviewer called it “absurd” and “impossible to imagine,” but the event has solid support from other sources.

Certainly, the number mattered to Furman. Sokolov remembered that his father would often point to his own tattoo and tell stories about it, but his mother was always discrete.

Eventually, he said, “she couldn’t sleep because it bothered her so much.”

Furman had her tattoo removed when she was in her 60s. I asked Gary why his mother’s number was said to be 34902. He said, “I have no idea.”

Either way, the love was real. Gary said that Lali doted on Gita for the rest of her life.