Late one night, in the year 1900, Roberto Columbo, an Italian lawyer living in New York's Little Italy neighborhood, secretly meets with police at the Carey Street Hotel to show them a threatening letter he received from the notorious Black Hand extortion gang. The letter indicates that the Black Hand is demanding that Roberto pay them protection money or face death. No sooner does Roberto begin to describe some of the gang members to the police than two mobsters enter the station and kill him. The murder devastates Roberto's wife Maria, who decides to return to Italy with her son Johnny. Eight years later, following the death of his mother, Johnny returns to New York vowing to avenge his father's death and end the Black Hand's operations. While looking for Black Hand gangsters, Johnny has a reunion with Isabella Gomboli, a childhood friend, who warns him that the mob is unstoppable and that he will be in great danger. Although Isabella's parents were killed by the Black Hand, she suggests that Johnny drop "La Vendetta" and form a citizen's league instead. Johnny rejects Isabella's suggestion, though, and insists on meeting with Moriani, former owner of the Carey Street Hotel, who was with his father the night he was killed. Shortly after Johnny's meeting with Moriani, Moriani is found dead in his hotel room. Hoping to steer Johnny away from trouble, police officer Louis Lorelli, a friend of Johnny's father, offers him a job in New Jersey and advises him to make a success of himself. Johnny eventually decides to take Isabella's advice and form a citizen's league when he discovers that Francesco, the son of tailor Benny Danetta, has been kidnapped by the Black Hand. Francesco is released soon after the first citizen's league meeting is convened, but Johnny is punished by the Black Hand for organizing the group and is given a severe beating. Later, a bomb is found on the steps of Carlo Sabballera's dry goods store. Johnny's investigation into the Black Hand leads to the arrest of George Allani, who is accused of placing the bomb in front of Sabballera's store. At Allani's trial, Carlo is about to identify the gangster as the culprit when he is given the death sign by some Black Hand men. The frightened store owner refuses to identify Allani, and, as a result, it appears that Allani will go free. At the last moment, however, it is revealed that Allani is using an assumed name, and that he is really George Tomasino, an Italian fugitive. The judge orders Tomasino's deportation, which gives Lorelli the idea to go to Italy to check Italian police records against his list of suspects. In Naples, Italy, Lorelli is shot and killed by Black Hand gangsters right after he mails a list of Italian criminals to Johnny. Back in New York, the Black Hand has kidnapped Isabella's younger brother Rudi, and is demanding the list of names as ransom. While attempting to rescue Rudi, Johnny is captured by the Black Hand. Johnny manages to escape by setting off a time bomb that kills everyone in the Black Hand headquarters except Caesar Xavier Serpi. Serpi later engages Johnny in a fight with a pickax, but Johnny kills him with a knife. With Lorelli's list safely delivered to the police, Johnny is confident that he has put an end to the Black Hand operations in New York.