The novel, set in the later days of Prohibition, tells the story of how Vito Corleone rose through the criminal underworld to become the most powerful Don in New York. Also, it tells of Sonny Corleone's inauguration into the family business and Tom Hagen's graduation from being an adopted member of the Corleone family before becoming the consigliere. The novel also reveals how Luca Brasi first became associated with the Corleones, and introduces a number of new characters, including the crime boss Giuseppe Mariposa.