''Marvellous.'' A.S. Byatt''Astonishing.'' John Gray''Luminous.'' Rose TremainI could take whichever I would of these paths.Sammy Mountjoy is an artist who has risen from poverty to see his pictures hung in the Tate Gallery. Swept into World War II, he is captured as a German prisoner of war, threatened with torture and locked in a cell of total darkness. He emerges transfigured by his ordeal, realising how his choices have made him the author of his life, interrogating religion and rationality, early loves and formative beliefs – and questioning freedom itself.