Author David Grann often writes about obsession. His stories feature people doing extraordinary, and often dangerous or morally questionable things, in pursuit of ambitious goals. He’s the author of the books “Lost City of Z,” “Killers of the Flower Moon,” and his newest, “The Wager.” Grann is also obsessive about the research and details he puts into his books. We talk to Grann in front of a group of students at Nelson High School in Happy Valley.