It is the turn of the century. Lieutenant Joe Petrosino of the New York Police Department is a man with an obsession. Believing that there is a secret society controlling organised crime in America, he aims to expose the Mafia. With disbelieving superiors, he alone must face the feared Don Vito Cascio Ferro. Would-be informers are too scared to talk, but Petrosino gets his first lead with the discovery of a brutally murdered body in a New York alley.