Every weekday at 8 a.m., Kevin Brock hefts a thick white ring binder onto a sleek, oval conference table. Labeled "Read Book," the deceptively plain folder houses the "Threat Matrix," a top-secret compendium of the most troubling reports of possible terrorist activity, drawn from the nation's 16 intelligence agencies. It is thicker than usual on a recent Monday morning, packed with 66 separate items that came in over the weekend. Brock, the principal deputy director of the National Counterterrorism Center, is about to brief some of the government's most senior officials on the latest threat information. -snip- Facing a wall...