From 1939 until 1945 the world was at war, and the leader of Germany, Adolf Hitler, tried to destroy the Jewish people in Europe. His followers, the Nazis, and those who supported them, murdered six million Jews including one and a half million children. They also killed a lot of other people, many of whom offered shelter to the Jews. We call this time of killing the Holocaust.

My grandfather was a Jew from Krakow in Poland. He left there long before that time, but his extended family didn’t and most of them perished.

Ten years ago I read a book about Janusz Korczak, a Polish Jewish doctor and children’s author who devoted his life to caring for young people. Over many years he helped run an orphanage for two hundred Jewish children. In 1942, when the Nazis murdered these orphans, Janusz Korczak was offered his freedom but chose to die with the children rather than abandon them.

Janusz Korczak became my hero. His story sowed a seed in my imagination.

On the way to writing Once I read many real life stories – diaries, letters, notes and memories of people who were young at the time of the Holocaust. Most of these young people died, but their stories survived, and you can read some of them in the following books.

The King Of Children by Betty Jean Lifton (biography of Janusz Korczak)

Salvaged Pages: Young Writers' Diaries Of The Holocaust, edited by Alexander Zapruder

The Hidden Children by Jane Marks

Words To Outlive Us: Eyewitness Accounts From The Warsaw Ghetto, edited by Michal Grynberg

Witness: Voices From The Holocaust, edited by Joshua M Greene & Shiva Kumar

A Childhood by Jona Oberski

Maus by Art Spiegelman

The Diary Of A Young Girl by Anne Frank

Born Guilty by Peter Sichrovsky

The Hidden Children by Howard Greenfeld

Children Of The Ghetto by Sheva Glas-Wiener

Konin: A Quest by Theo Richmond

The Boys by Martin Gilbert

Flares Of Memory: Stories Of Childhood During The Holocaust, edited by Anita Brostoff with Sheila Chamovitz

Yiddishland by Gerard Silvain & Henri Minczeles

Children With A Star by Deborah Dwork

Ghetto Diary by Janusz Korczak

As with Once, I couldn’t have written this story without first reading many books about the Holocaust. Books full of the voices of the real people who lived and struggled and loved and died and, just a few of them, survived in that terrible time.

I also read about the generosity and bravery of the people who risked their lives to shelter others, often children who were not members of their family or faith, and by doing so saved them.

Here are some of the books that helped me write Then. I hope you get to read some of them and help keep alive the memory of the real people and their real stories.

Witnesses Of War: Children’s Lives Under The Nazis by Nicholas Stargardt

The Righteous: The Unsung Heroes Of The Holocaust by Martin Gilbert

Holocaust Journey by Martin Gilbert

The Lost by Daniel Mendelsohn

The Mascot by Mark Kurzem

Bad Faith by Carmen Cahllil

Into That Darkness by Gitta Sereny

Albert Speer: His Battle With Truth by Gitta Sereny

The German Trauma by Gitta Sereny

Night by Elie Wiesel

If This Is A Man by Primo Levi

The Truce by Primo Levi

If Not Now, When? by Primo Levi

Eichmann In Jerusalem by Hannah Arendt

Nazi Hunter: The Wiesenthal File by Alan Levy

Long Shadows: Truth, Lies And History by Erna Paris

Stalingrad by Anthony Beever

Child Of The Holocaust by Jack Kuper

I Didn’t Say Goodbye: Interviews With Children Of The Holocaust by Claudine Vegh

The Avengers: A Jewish War Story by Rich Cohen

Lest Innocent Blood Be Shed: The Story Of The Village Of Le Chambon And How Goodness Happened There by Philip P Hallie

The Lost Childhood by Yehuda Nir

A History Of The Jews In The Modern World by Howard M Sachar

There are of course many other real stories of the Holocaust in many other books. And if you have a Jewish or Holocaust museum near you, you'll find a wealth of memories in their archives that are perhaps not published elsewhere. If there isn't one near you, most have websites containing unforgettable personal stories. Putting 'Holocaust Museum' into Google or another search engine will give you many sites to explore.

Once and Then are my imagination trying to grasp the unimaginable. The stories in these books and archives are the real stories.

(For teachers and other interested readers, there are also Once and Then Teachers and Readers Notes on the Puffin website.)

The real life stories in the books mentioned above were also an important background to this third part of the trilogy. As were the real life stories of the people and communities caught up in the terrible bushfires that swept through parts of Victoria, Australia in February 2009. Many of those stories were recorded in the extensive media coverage of that time, and many others live on in the following books:

Black Saturday edited by John McGourty

A Future In Flames by Danielle Clode

Worst Of Days by Karen Kissane

Inferno by Roger Franklin