At 8:46 A.M. on a beautiful Tuesday morning, a Boeing 767 flew straight into the World Trade Center. Most people, when they heard the initial reports of a plane flying into Tower One, immediately assumed it was a small, private plane whose pilot made a tragic error. But when the second jet crashed into Tower Two about fifteen minutes later, everyone knew the crashes were no accident. The United States was under attack by an unknown enemy.

The first plane, American Airlines Flight 11, en route from Boston to Los Angeles, had ninety-two passengers on board, including five Arab men assumed to be the hijackers. It crashed into Tower One between the ninety-fourth and ninety-eighth floors. United Airlines Flight 175, the second plane, was also en route to Los Angeles from Boston; it had sixty-five passengers on board, including five hijackers. At 9:03 A.M., banking hard to...