Donnie Brasco
The story of the FBI agent whose undercover name was Donnie Brasco, which had a great movie adaptation in ‘97 with Al Pacino and Johnny Depp.
It is a great read, very enjoyable, with a simple and matter-of-fact style.
Interestingly, the author said that the movie was 80-85% accurate, most of the storyline from the book is preserved.