This is a biography of John O'Neill, who was basically the FBI's head of counterterrorism in the New York office until 2001, when he retired and went to work as the head of security at the World Trade Center, where he was about two weeks into the job when he was killed in the September 11th terrorist attacks.
The book details O'Neill's life from his time growing up in New Jersey, dreaming of becoming an FBI agent, to his death in 2001. The book shows him as a complicated figure who could be brash and overbearing at one moment and kind and generous the next. He would roll over people one second and seek their approval the next. The book does detail his messy personal life, dating (and making promises of marriage) to multiple women, while still being married to his first wife because of his Catholic faith. The book really focuses on how he was one of the first people to recognize and warn government officials of the threat of Al-Qaeda and worked to build a case against Osama Bin Ladin so the FBI could go into Afghanistan and grab him. It also detailed the way he butted heads with people in the FBI and how his penchant for bending the rules, and his personal life caused him to be passed over for promotions and ultimately forced out of the FBI. The book portrays O'Neill as really being married to his work, and being someone who rarely slept and was obsessive about getting everything perfect.
The book is a bit incomplete in that, while it does detail how O'Neill butted heads with the Ambassador of Yemen when investigating the bombing of the USS Cole, and his fights with FBI brass, it does not go into the infighting between O'Neil and the CIA agents in the "Bin Ladin Unit", and only touched on the refusal of the CIA to share information with the FBI (and pretty much specifically with O'Neill). The book also has a lot of inaccuracies about what happened on September 11th, such as misidentifying the pilot of Flight 11, attributing the threats intended for the passengers of Flight 11 that were broadcast to Air Traffic Control as being made by the hijacker pilot of Flight 175, and getting some parts of the timeline wrong. The book was published in 2002, so certainly not all of the information that has been revealed since it was written was widely known when it was being written, but some of the mistakes could have been avoided with a little research and better editing. The does, however, provide some details about how O'Neill died that I have not seen widely reported.
Overall, the book is a good look at a man with a complex life. The book is about 400 pages of substantive text, and then about 30 pages of notes. It is not an easy read, but it is not extremely difficult to get through either. People who read quickly should be able to get through it in a week or less, depending on how much time they have to read. I definitely recommend it.