In The Living Unknown Soldier (Henry Holt), the French historian Jean-Yves Le Naour tells the story of “Anthelme Mangin,” an amnesiac discovered wandering on the train-station platform in Lyon in February 1918. He was assumed to be a prisoner of war repatriated by the Germans because they did not want to care for him. Obviously traumatized by whatever he had experienced, “Mangin” (he had to be called something) could hardly speak and was never identified, though the search for his relations, which is the subject of Le Naour’s book, went on for years. The case of the mysterious soldier was publicized widely, and various people came forward to claim him as their lost son, brother, husband or lover. The lengths to which these claimants went, against all evidence, to prove that Mangin was in fact their absent loved one, is heartbreaking. The story is suffused with grief and leads Le Naour into a wide-ranging discussion of what The Missing meant to those who were left behind. Mangin lived out his days in an asylum for the mentally ill and died in 1942. In a horrifying footnote, Le Naour reveals that during the Second World War, more than forty thousand inmates of French psychiatric institutions starved to death in hospitals that were meant to care for them.