Book excerpt: As the bombs rain down in the Second World War, one young girl is evacuated to the English countryside. Struggling to make sense of her new wartime life, she is given a copy of a book of ancient Norse myths and her inner and outer worlds are transformed. Linguistically stunning and imaginatively abundant, Byatt’s mesmerising tale - inspired by the myth of Ragnarok - is a landmark piece of storytelling from one of the world's truly great writers.