A hundred years ago, at the height of the First World War, John Tolkien, a 25-year-old former lieutenant with the Lancaster Fusiliers, went walking with his wife, Edith, in the Yorkshire countryside. He’d recently returned to Britain from the battlefields of France, after acquiring a case of trench fever. Both the condition and his harrowing experiences in the Battle of the Somme, which claimed the lives of some 600,000 allied soldiers, had weakened him. The carnage continued after he left, decimating nearly his entire battalion. “By 1918,” he wrote later, “all but one of my close friends was dead.” As he walked with his wife, they came to a glade flowered with hemlock. Tolkien sat down to rest. His wife, who was struggling to restore his spirits, began to dance for him among the flowers.