What is a summary of the book 'Once' by Morris?

'Once' by Morris Gleitzman is a novel set during the Holocaust, following the story of a young Jewish boy named Felix. Felix has been left in an orphanage by his parents and is determined to find them, believing they are coming back for him. As he embarks on a journey to find his parents, he encounters the harsh realities of the war and the atrocities committed against the Jewish people. The book explores themes of innocence, hope, and resilience in the face of adversity.