In the late nineteenth century, private detective James McParland attracted fame and controversy. Gifted and ambitious, McParland rose quickly through the ranks of the Pinkerton Detective Agency, then the premier agency of its kind. In the 1870s, he infiltrated, spied upon, and ultimately helped to convict Irish-American miners in Pennsylvania. The execution of twenty men implicated in terrorism by McParland led to both his praise and vilification. Leaders of industry saw him as a hero; trade leaders saw him as management's weapon against unions. His story casts light upon the methods and political uses of for-hire detectives during the infancy of U.S. policing.

Born in Ireland in 1843 and drifting through jobs in his youth, McParland was a circus barker at one point in his twenties. Restless for a new start at the age of twenty-four, he joined in the waves of Irish emigration to the United States...