Europe, 1940s: Imprisoned in the Mauthausen concentration camp in Austria, Spanish fighter and photographer Mateo Baca is ordered to process images of the camp and inmates for a handful of photo books being made for presentation to top Nazi figures. Just five books in total, or so the officials think ...

Mateo manages to make a secret sixth book and, with the help of a local woman, Lena Lang, it remains hidden until the end of the war.

Australia, present day: When thirteen-year-old Hannah Campbell's Yugoslavian grandfather, Nico Antonov, arrives in Australia to visit his family, one of the gifts he brings with him is an intriguing-looking parcel wrapped in a flour sack, which Roza, Hannah's mother, quickly hides.

Later, Hannah sneaks off in search for the mysterious package. She is horrified to find in it a photo book full of ghastly historical photographs of a terrible place full of people suffering.

At first Hannah has little context for what she sees, but over the years, as she experiences love, grief and trauma, she understands what these photos came to mean, for herself, her freedom and for those who risked their lives to 'bear witness' to history?