"'They were there at the beginning of the war, but they were gone by the end. I suppose they died in the camps.' That's all young Michael Rosen, born in England just after the end of the Second World War, was told about the six great-aunts and great-uncles who had been living in Poland or France at the beginning of that war. This wasn't enough for him. So, as an adult, he started to search. He asked relatives for any papers they might have. He read...