Sunday night, as U.S. bombers and cruise missiles attack targets in Afghanistan, Osama bin Laden released a videotape calling on Muslims worldwide to join his war on America. Next to bin Laden was his close association, an Egyptian named Ayman al-Zawahiri, a man who is certainly as important to the terror network as bin Laden himself.

Tonight on FRONTLINE, the full story of these two men, the story of how the seeds of their hatred for America were sown not in Afghanistan but in two of the U.S.'s greatest allies in the Islamic world, Egypt and Saudi Arabia, and the story of how they joined forces to pursue a common enemy.