This is a very uneven and disappointing work.
Many details about Det. Joseph Petrosino, but most of the research on La Mano Nera comes from contemporary newspaper articles.
He never really answers the question " What was the Black Hand?".
The author, not being of Italian decent, understands little about the dynamics of different groups in the era before WWI.
He uses "Sicilian" very freely to describe many people.
He hardly mentions Neapolitans.
If you really want to know about pre-WWI US organized crime see:
The Honored Society - Norman Lewis
The First Family – Mike Dash
The Origin of Organized Crime in America: The New York City Mafia, 1891–1931 - David Critchley
The Business of Crime: Italians and Syndicate Crime in the United States - Humbert S. Nelli