William E. Dodd was an academic historian, living a quiet life in Chicago, when Franklin D. Roosevelt appointed him United States ambassador to Germany. It was 1933, Hitler had recently been appointed chancellor, the world was about to change.

Had Dodd gone to Berlin by himself, his reports of events, his diary entries, his quarrels with the State Department, his conversations with Roosevelt would be source material for specialists. But the general reader is in luck on two counts: First, Dodd took his family to Berlin, including his young, beautiful and sexually adventurous daughter, Martha; second, the book that recounts this story, “In the Garden of Beasts,” is by Erik Larson, the author of “The Devil in the White City.” Larson has meticulously researched the Dodds’ intimate witness to Hitler’s ascendancy and created an edifying narrative of this historical byway that has all the pleasures of a political thriller: innocents abroad, the gathering storm.

When the Dodds arrived in Germany in July 1933, storm troopers were beating American tourists bloody on the streets. Jews (1 percent of Germany’s population) were targets of brutal violence and ever tightening social restrictions.

Martha Dodd found life in Berlin entirely charming. Many men courted her and found her eagerly responsive. She was enthralled with the Nazi movement: “I felt like a child, ebullient and careless, the intoxication of the new regime working like wine in me,” she wrote in her memoir. To a friend she said, “We sort of don’t like the Jews anyway.”...