HarperCollins executive editor David Hirshey bought a book that is said to be the first exhaustively researched one about the young Arabs who took over and piloted the planes that hit New York and Washington. It's by Terry McDermott, a Los Angeles Times terrorism expert who is described as one of the most knowledgeable in the field, and it will be called Perfect Soldiers: The Men of Al Qaeda and the Plot That Brought Jihad to America. McDermott will trace how the terrorists, mostly from comfortable middle-class backgrounds in Saudi Arabia, turned themselves into suicide pilots. It was a world rights sale made by editor-turned-agent Paul Bresnick and was being sold vigorously by Harper's Brenda Segel in London.