Do our ancestors play a meaningful role in our lives today? Can they make their presence felt through the agency of serendipity, those marvelous coincidences that defy our rational attempts to explain them away? In 2009, radio journalist Joe McHugh set out on a journey to find the family of an African-American woman named Helen who cared for him when he was a young child and who helped his family survive a terrible tragedy. Armed only with her first name and a passing reference to a house fire in a letter written in 1952, he visited the places that shaped the early lives of his parents,...