Karen Kirsten can still feel the wave of conflicting emotions that hit her as a child when she discovered her family had been lying to her for years.

There were tears, screams, nervous laughter, shaking and even some hiccupping.

She was 13 years old and an innocent question about her grandparents had led to her mother Joasia to admit to a secret she had been forced to hide; the people Joasia thought were her parents were actually her aunt and uncle.

Joasia’s biological father was a man Karen had been introduced to a few months earlier as “Uncle Dick” while on a family trip to Canada. Her biological mother, Irena, had been shot and killed by the Nazis.

Karen is now in her fifties —she’s been trying to unravel her family’s secrets through ten long years of research and accepts there are questions to which she will never have answers: why did a Ukrainian SS guard who thought nothing of killing women, save the infant Joasia by taking her to a convent?

Why did Alicja, the woman she had considered her grandmother, claim she couldn’t sew when she later revealed she’d held onto her life in Auschwitz by making a nightdress out of scraps? Why did Dick really give up his daughter?

Her book Irena’s Gift is the result of that research. It is a knotty complicated work about two couples — four secular Polish Jews — whose lives were upended by Hitler and the Nazis. It is about the secrets and the walls put up by those who survived the worst man can inflict on man. And it is about how trauma can trickle down the generations.

“All of my family were hiding secrets behind this wall of silence,” says Karen, an Australian who lives in America. “People want simple answers to life and Holocaust books which show happy survivors, but I discovered a multilayered story.

Joasia in Dachau, Germany, in 1946 COURTESY OF KAREN KIRSTEN

Joasia in the town of Dachau (Photo: Karen Kirsten)

“Yes, in many ways my mother was happy. She was an optimistic, bubbly person with legions of friends. But there was another side to her. For people who have endured trauma, the truth is often to be found in what they don’t say.”

Karen grew up in the Melbourne suburb of Warranwood where she never really thought about her family being Jewish. In fact, she nicknamed her grandparents’ Polish and Hungarian friends “The Polish Circus”.

When she asked her grandmother what the numbers etched onto her arm were, she was told: “It’s our phone number, so I won’t forget it.” But she always knew, in the way that children often do, that the grown-ups were withholding the truth.

Karen also knew that while her grandmother Alicja adored her and her sister Jacqui, she had barely a good word to say to their mother, Joasia.

Meanwhile, their grandfather Mietek would often stare for hours in complete silence at a wall in their living room that was packed with books about the Holocaust.

Karen was aged nine when a letter arrived from Canada from a man called Zdzisław Przgoda revealing that he was Joasia’s father. His late wife Irena was Joasia’s mother and Alicja’s sister, he wrote.

Joasia had been sneaked out of the Warsaw ghetto in a rucksack and then hidden in a convent. The rest of the family was sent to concentration camps. We learn in the book why he didn’t reunite with Joasia after the war.

While Alicja must have, in some ways, been relieved that this secret was out she made Joasia promise not to tell Karen and her sister unless they asked whether she was adopted. Two years later, they asked that very question.

In the meantime, when Joasia took her family to meet her father, the children were told that he was simply a relation who should be known as “Uncle Dick”. And so, the secrets and lies went on.

But when Steven Spielberg’s film Schindler’s List came out in 1993, everything changed.

Alicja and Mietek wedding

Alicja and Mietek on their wedding day (Photo: Karen Kirsten)

“My grandmother asked me to take her to see the film and a week or so later she asked me to take her for dinner. There, for the first time, she talked about what had happened during the war,” recalls Karen.

“I was eating a prawn risotto with white tomatoes when she started telling me about Mengele. I have since learned that Holocaust survivors often tell their grandchildren things they can’t tell their children.”

It was a lot of knowledge for Karen to hold, and it was only when she moved to a Jewish neighbourhood in America that she became more actively curious about her family history.

Karen went on: “My neighbours were Jews and they seemed different from the Hungarians and Poles I met in my grandparents’ living rooms. With them, I had never heard the word synagogue, but now it came up all the time.”

She interviewed her grandmother for several days — by then her grandfather was dead — to ensure the story, or as much of it as Alicja she was willing to share, was written down.

“Just before I flew back to America my grandmother said, ‘I’m worried this is going to happen again,’” recalls Karen. “I promised that I would tell her story.”

But then life and a new career got in the way.

Seven years later, she stumbled on a film clip from Dachau that had been restored by London’s Imperial War Museum in which a “Jewish leader” was interviewed. It was the man she thought of as her grandfather, Mietek.

Karen said: “He was asked ‘Why were you here as a prisoner?’ and I heard him say, in English, ‘Because I am a Jew’. The whole thing shocked me deeply. I had never heard him say the word Jew before and here he was speaking as a representative of the Jewish community. And he did it so eloquently.

Joasia and Karen in Poland. Poland 2012.COURTESY OF KAREN KIRSTEN

Joasia and Karen in Poland (Photo: Karen Kirsten)

“Then, of course, I thought back to all the clues that had been staring me in the face; the way he would stare at walls for hours, and how I had never connected that to depression and surviving the Shoah.”

His testimony, recorded for a British Ministry of Information documentary, is harrowing. “They treated us worse than the worst beasts,” Mietek says. Revealing that all of his friends had been sent to the crematorium, he adds: “The crematorium, that was the nice death. They tortured us in other ways that were much worse. You were hanged, you were beaten to death with whips.”

The video prompted Karen to try and unravel her family’s history while at least some of its members were still alive to remember events. One highlight of her journey was reuniting her mother — who became an evangelical Christian — with the nuns who hid her from the Nazis.

One of the hardest parts was walking in the footsteps of her grandparents and learning why Dick had given up his daughter. Throughout the book, there is enormous empathy for those irrevocably damaged by what had happened to them.

Today, she works partly as a Holocaust educator and has become a fixture in Poland in the town just outside Warsaw where her mother was killed. Her book also recognises the way the trauma bleeds down the generations.

“I recently read Anne Berest’s The Postcard. She compares being the child of a Holocaust survivor to breathing in second-hand smoke,” says Karen. “If you grow up around survivors you can’t help being affected by their experiences, but some of those effects reveal themselves much later.

“It is easy to become numb to war, to lock it out. But I wanted to tell how war affected one family, to humanise numbers like: 1.1million murdered in Auschwitz. There are 35 million refugees in the world today but the numbers don’t mean much unless we individualise people.

“So, I hope that if someone reads the book and learns that the grandmother who used to squat with me at rock pools by the beach also traded her wedding ring for a piece of bread to stave off starvation, it gives them pause for thought.”

‘Irena’s Gift’ by Karen Kirsten (Mardle Books) is out this week