Rudy Giuliani emerged from the smoke of 9/11 as the unquestioned hero of the day: America's Mayor, the father figure we could all rely on to be tough, to be wise, to do the right thing. In that uncertain time, it was a comfort to know that he was on the scene and in control, making the best of a dire situation.

But was he really?

Grand Illusion is the definitive report on Rudy Giuliani's role in 9/11—the true story of what happened that day and the first clear-eyed evaluation of Giuliani's role before, during, and after the disaster.

While the pictures of a soot-covered Giuliani making his way through the streets became very much a part of his personal mythology, they were also a symbol of one of his greatest failures. The mayor's performance, though marked by personal courage and grace under fire, followed two terms in office pursuing an utterly wrongheaded approach to the city's security against terrorism. Turning the mythology on its head, Grand...