What is the theme in Shadowlands by William Nicholson?

Love and passion/change and transformation are all themes in this book. At the beginning of Shadowlands, both Joy and Lewis are rather unhappy in their own way. Joy is stuck in a bad marriage. Her husband, Bill, is an alcoholic and has had numerous liaisons during their marriage. She finds solace only in Lewis' letters to her and in his published books. When she comes to England on vacation with her son, Douglas, Joy finally meets the man behind the letters. They grow closer, though Lewis is much more stiff and formal than she is. But after Joy moves to England, and Lewis marries her "technically" so she can stay in the country, their relationship deepens. It blooms into love when Joy becomes ill with bone cancer, and Lewis and Joy realize that they will soon be losing each other.