It follows Joe Petrosino, a courageous NYPD cop who unflinchingly went after a ruthless gang that came out of Italy and into America (whose calling card was a black hand) which kidnapped people and then extorted money from their families. They were loathed by law-abiding Italian families who were frightened but nevertheless helped Petrosino behind the scenes when they could as the viciousness of the gang of thugs knew no boundaries.