Thomas Cook has always been drawn to dark places, for the powerful emotions they evoke and for what we can learn from them. These lessons are often unexpected and sometimes profoundly intimate, but they are never straightforward. With his wife and daughter, Cook travels across the globe in search of darkness—from Lourdes to Ghana, from San Francisco to Verdun, from the monumental, mechanized horror of Auschwitz to the intimate personal grief of a shrine to dead infants in Kamukura, Japan. Along the way he reflects on what these sites may teach us, not only about human history, but about...