A New Yorker writer investigates the life and career of his hit-man great-uncle and the impact on his family.

Growing up in a household as generic as Midwestern Jews get, author Eric Konigsberg always wished there was something different about his family, something exotic and mysterious, even shocking. When he was sent off to boarding school, he learned from an ex-cop security guard that there was: His great-uncle Harold, in prison in upstate New York, was a legendary Mafia enforcer, suspected by the FBI of upwards of twenty murders.

Konigsberg had uncovered a shameful, long-hidden...