The first time I saw Leni Riefenstahl’s photographs was in the library at Queen’s University Belfast. I was looking for a different book. But this one caught my eye: a worn red hardback with the single word “Olympia” printed on the spine. Inside the book were black and white photographs of athletes in action: running, jumping, swimming, sailing, throwing the discus. They were competitors in the 1936 Berlin Olympics, which Riefenstahl had filmed. Such moments take on personal significance only in hindsight. I couldn’t have known, back then, that this chance discovery in a library would be the springboard for...