Esther Safran Foer — though she will tell you in her book that she is very different from her mother — is a bit of a magpie, a collector and a hoarder. The collections range from pieces of dirt carefully preserved in a series of Ziploc bags, to pages and pages of files and family trees.

If you think hers is a familiar name, you are right: she is the mother of the novelist Jonathan Safran Foer, author of the best-selling Everything is Illuminated; and his two brothers, Franklin and Joshua, who are also well-known writers and journalists in the US.

In I Want You To Know We’re Still Here, Esther Safran Foer has written part memoir, part thriller and part mystery. It is the story of her own family, full of historical gaps, some of which she has filled in the course of more than two decades of dedicated research — filling a lot of those Ziploc bags along the way.

On the phone from her home in Washington DC, Safran Foer agrees that “the mystery part is certainly true. I did feel like a detective, and I was continually finding missing pieces and putting them in the back of my mind to put together later. It wasn’t like one thing happened after another, but I was able to consolidate the information —and I didn’t expect all the pieces to lead me where they led me, that I would be able to unravel as much as I did.”

So to the bare facts of her story, that which she knew at the start of her investigations. She knew that she was the daughter of Ethel and Louis Safran, both Holocaust survivors from central Europe, and that she herself had been born in Poland in 1946; she knew that the family had arrived in America in 1949 and that her father had committed suicide in 1954, and that her mother had remarried after his death.

She herself became a PR working for various high-profile American politicians, and latterly was the chief executive of one of Washington’s best known synagogues, Sixth and I, which operates as a cultural hub in the nation’s capital.

“I had grown up surrounded by ghosts”, Safran Foer writes. The primary ghost was her father, whose wartime experiences were a closed book to Esther and her brother. But when she was in her early 40s, preparing to give a talk at a local synagogue, she decided it was time to find out a little more.

So she sat her mother down in her kitchen and asked about her father. “My mother took a sip of the instant coffee that she loved and casually mentioned that my father had been in a ghetto with his wife and daughter. He’d been on a work detail when they were both murdered by the Nazis. Absolutely stunned, I blurted out, ‘He had a wife and daughter? Why haven’t you ever told me this before?’”

So began Safran Foer’s search for the name of her previously unknown half-sister, a search which led her to Ukraine and a difficult and emotional meeting with the family which had sheltered her father during the Holocaust.

Along the way she discovered — via DNA testing, forensic genealogical research, and internet networking — numerous family members she didn’t know she had. Trips to Brazil and Israel helped her find some of these relatives, although it must be said that some of this information is provided in the book in a blur of relationships, which frequently leave the reader as clueless at the end of the chapter as at the beginning.

Still, amid the blizzard of names and discoveries, Safran Foer often packs a hefty emotional punch. One such occasion is on a visit to Haifa where she meets 90-year-old Chaim Voitchin. On being shown a map of the town where her father came from, Trochenbrod, he at first professed ignorance. Then he offered: “I was married to Raizel Bisker, but no-one knows”.

This meant that Voitchin, like Safran Foer’s father, was yet another of the vast number of Jews who had married twice and sometimes three times, making it fiendishly difficult and complicated to track down who was who. Safran Foer discovered the importance of “asking the right question… in Trochenbrod, no-one used last names. They all had nicknames. My father wasn’t known as Louis Safran or Leibel Safran. He was Leibel from Lysche, the village he lived in after Trochenbrod.”

Perhaps the most poignant part of the book is when Safran Foer finally discovers her father’s heartbreaking suicide notes, written in Yiddish and “Yinglish”. They don’t answer the central question of why he could not survive in America — and Safran Foer is still not really sure what happened to him during the Holocaust, or where he was, apart from the time he was hidden by Ukrainian Christians.

“My mother never really talked about it”, she says. “He was 44 years old, and all she said was that “he was always running’”. Perhaps he simply ran out of road.

Safran Foer’s mother, the indomitable Ethel, died in December 2018, aware of all her daughter’s research and discoveries. Her death, says Safran Foer, enabled her to say some things in the final stages of the book that she had been unable to discuss with her mother.

If she has one message from her experience to pass on to others, she says it is to start to ask questions as early as possible. Safran Foer freely acknowledges that she has by no means found every piece of the jigsaw. “I have not found the absolute truth, but what I have found has given me peace. None of us will ever know about what happened in these terrible places, but I found more than I had ever hoped to find.”

I Want You To Know We’re Still Here by Esther Safran Foer is published by Harper Collins on April 22 at £20