This is an extraordinary book telling a terrible story beautifully and sensitively, and with hope and kindness.

Mizuki is sorry to see her grandfather so sad and urges him to tell her why he is full of such guilt and regret for something that happened to him such a long time ago.

He takes her back to 1945 where, as a teenager living in Hiroshima, he was with his friend Hiro as the horrific nuclear bomb is dropped. He recalls the blinding flash, the devastation and the desperate search for family.

The two teenage boys search for Keiko, Hiro's five-year-old sister and then seek safety. But they are forced to separate when Mizuki's grandfather goes for help. He is never reunited with Keiko and is haunted by the fact that he abandoned her.

He leaves origami paper cranes with his address in the hope that if Keiko survived she would be able to find him. But he never hears from her.

The story is told through prose and also free verse, and illustrated throughout. It's a powerful, upsetting and challenging read though ultimately leaves the reader with a sense of hope.