With an outdoors-oriented vacation to Montana winding down, Justice Mark Dillon, his wife and four children were looking for something else to do. On the last day, they stumbled on a ghost town, starting the 54-year-old New York appellate judge on the road to a chronicle of the Wild Wild West’s vigilante movement.

Dillon, a Second Department justice from the far less rugged lands of Westchester County, had not been a western history buff before his trip to Montana. But he was intrigued by monuments and exhibits he saw related to the vigilante movement of the nineteenth century in the lawless frontier territory. His interest eventually led to a book—his first—about vigilantism, told from a legal perspective.