One Drop, by Bliss Broyard

Subtitled "My Father's Hidden Life: A Story of Race and Family Secrets," Broyard's memoir of her experience discovering, then researching her father's hidden ethnicity was one of the most engaging non-fiction books I've read in ages. Equal parts soul-searching memoir, deep historical research, and family story, it kept me involved by jumping back and forth between present, past, and far past. Great book.