I first ran into this book when an excerpt of it was inserted in "The Mammoth Book of the Mafia". At that time I read it as just a short peek into the life of the wiseguys, but when I bought my Kindle, I downloaded a sample of it and then bought the book.
Joe Pistone, an FBI agent, didn't really aim for six years in the Mafia, far from it. He started a six-month undercover stint into the stolen trucks business, trying to get a crack into the organized racket. What happened was that his undercover role started gaining the trust of criminals, and within a year and a half, he had the trust of his first mobster friends.
Posing as a jewel thief and shylock, Pistone aka Donnie Brasco started getting his toe into the door of ever bigger operations, such as vending machines, gambling clubs, and the like. Groomed by wiseguy Benjamin "Lefty Two Guns" Ruggiero, he learned how to pose as a connected man, one close to the Mob but not yet a made member. He managed to work his way up in the Cosa Nostra, eventually gaining the trust of a Captain.
Only after Donnie was assigned a hit to do, he had to leave his cover, and go back to the FBI to start the legal proceedings. Such was his career as Donnie Brasco that the Mafia canceled the 500,000 dollar contract on him, and the wiseguys he cheated went on record saying he beat them square and fair. Dozens of convictions resulted from his work.
I recommend this book to any student of organized crime, especially one who likes to see how the choreography of the Mob works - who talks to who, how does one talk, what not to do ever etc. A wonderful book by a very brave man.