I never knew my uncle. Marvin Risen, my father’s brother, died long before I was born. He was an FBI agent in Nashville and was killed in a plane crash in 1943. But decades later, when I was growing up, something about Marvin’s death still troubled my family. My parents often talked about how they had never been given any answers about Marvin’s death, and that led them to speculate wildly, trying to connect the dots. They openly questioned whether he had been the victim of wartime sabotage. His plane crashed in the middle of World War II, and his...